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A quick and simple guide to get started with VerneMQ
VerneMQ is a high-performance, distributed MQTT message broker. It scales horizontally and vertically on commodity hardware to support a high number of concurrent publishers and consumers while maintaining low latency and fault tolerance. To use it, all you need to do is install the VerneMQ package.
Choose your OS and follow the instructions:
It is also possible to run VerneMQ using our Docker image:
If you built VerneMQ from sources, you can add the /bin
directory of your VerneMQ release to PATH
. For example, if you compiled VerneMQ in the /home/vernemq
directory, then add the binary directory (/home/vernemq/_build/default/rel/vernemq/bin
) to your PATH, so that VerneMQ commands can be used in the same manner as with a packaged installation.
To start a VerneMQ broker, use the vernemq start command in your Shell:
A successful start will return no output. If there is a problem starting the broker, an error message is printed to STDERR
.
To run VerneMQ with an attached interactive Erlang console:
A VerneMQ broker is typically started in console mode for debugging or troubleshooting purposes. Note that if you start VerneMQ in this manner, it is running as a foreground process that will exit when the console is closed.
You can close the console by issuing this command at the Erlang prompt:
Once your broker has started, you can initially check that it is running with the vernemq ping command:
The command will respond with pong
if the broker is running or Node <NodeName> not responding to pings
in case it’s not.
As you may have noticed, VerneMQ will warn you at startup when your system’s open files limit (ulimit -n
) is too low. You’re advised to increase the OS default open files limit when running VerneMQ. Read more about why and how in the Open Files Limit documentation.
Welcome to the VerneMQ documentation! This is a reference guide for most of the available features and options of VerneMQ. The Getting Started guide might be a good entry point.
For a more general overview on VerneMQ and MQTT, you might want to start with the introduction.
For downloading VerneMQ see Downloads.
VerneMQ comes with a simple file-based password authentication mechanism which is enabled by default. If you don't need this it can be disabled by setting:
Per default VerneMQ doesn't accept any client that hasn't been configured using vmq-passwd
. If you want to change this and accept any client connection you can set:
Warning: Setting allow_anonymous=on
completely disables authentication in the broker and plugin authentication hooks are never called! See more information about the authentication hooks .
In a production setup we recommend to use the provided password based authentication mechanism or implement your own authentication plugins.
VerneMQ periodically checks the specified password file.
The check interval defaults to 10 seconds and can also be defined in the vernemq.conf
.
Setting the password_reload_interval = 0
disables automatic reloading.
Both configuration parameters can also be changed at runtime using the vmq-admin
script.
vmq-passwd
is a tool for managing password files for the VerneMQ broker. Usernames must not contain ":"
, passwords are stored in similar format to .
How to use vmq-passwd
Options
-c
Creates a new password file. If the file already exists, it will be overwritten.
-D
Deletes the specified user from the password file.
-U
This option can be used to upgrade/convert a password file with plain text passwords into one using hashed passwords. It will modify the specified file. It does not detect whether passwords are already hashed, so using it on a password file that already contains hashed passwords will generate new hashes based on the old hashes and render the password file unusable. Note, with this option neither usernames or passwords may contain
":"
.
passwordfile
The password file to modify.
username
The username to add/update/delete.
Examples
Add a user to a new password file: (you can choose an arbitrary name for the password file, it only has to match the configuration in the VerneMQ configuration file).
Delete a user from a password file
Acknowledgements
The original version of vmq-passwd
was developed by Roger Light (roger@atchoo.org).
vmq-passwd
includes :
software developed by the [OpenSSL
cryptographic software written by Eric Young
(eay@cryptsoft.com)
software written by Tim Hudson (tjh@cryptsoft.com)
VerneMQ comes with a simple ACL based authorization mechanism which is enabled by default. If you don't need this it can be disabled by setting:
VerneMQ periodically checks the specified ACL file.
The check interval defaults to 10 seconds and can also be defined in the vernemq.conf
.
Setting the acl_reload_interval = 0
disables automatic reloading.
Both configuration parameters can also be changed at runtime using the vmq-admin
script.
Topic access is added with lines of the format:
Only one space should be put between the topic and the preceeding keyword. Extra spaces will be interpreted as part of the topic! Also note that the ACL parser doesn't accept empty lines between entries.
The access type is controlled using read
or write
. If not provided then read and write access is granted for the topic
. The topic
can use the MQTT subscription wildcards +
or #
.
The first set of topics are applied to all anonymous clients (assuming allow_anonymous = on
). User specific ACLs are added after a user line as follows (this is the username not the client id):
It is also possible to define ACLs based on pattern substitution within the topic. The form is the same as for the topic keyword, but using pattern as the keyword.
The patterns available for substitution are:
%c
to match the client id of the client
%u
to match the username of the client
The substitution pattern must be the only text for that level of hierarchy. Pattern ACLs apply to all users even if the user keyword has previously been given.
Example:
VerneMQ currently doesn't cancel active subscriptions in case the ACL file revokes access for a topic.
Anonymous users are allowed to
publish & subscribe to topic bar.
publish to topic foo.
subscribe to topic all.
User john is allowed to
publish & subscribe to topic foo.
subscribe to topic baz.
publish to topic all.
Project]() for use in the OpenSSL Toolkit.
As well as being available as packages that can be installed directly into the operating systems, VerneMQ is also available as a Docker image. Below is an example of how to set up a couple of VerneMQ
To use the provided docker images the VerneMQ EULA must be accepted. See Accepting the VerneMQ EULA for more information.
Sometimes you need to configure a forwarding for ports (on a Mac for example):
This starts a new node that listens on 1883 for MQTT connections and on 8080 for MQTT over websocket connections. However, at this moment the broker won't be able to authenticate the connecting clients. To allow anonymous clients use the DOCKER_VERNEMQ_ALLOW_ANONYMOUS=on
environment variable.
Warning: Setting allow_anonymous=on
completely disables authentication in the broker and plugin authentication hooks are never called! See more information about the authentication hooks here.
This allows a newly started container to automatically join a VerneMQ cluster. Assuming you started your first node like the example above you could autojoin the cluster (which currently consists of a single container 'vernemq1') like the following:
(Note, you can find the IP of a docker container using docker inspect <CONTAINER_NAME> | grep \"IPAddress\"
).
To check if the above containers have successfully clustered you can issue the vmq-admin
command:
To use the VerneMQ pre-built packages and Docker images you have to accept the VerneMQ EULA. Make sure to read and understand the EULA before accepting it.
Accepting the EULA for OS packages can be done by either changing the accept_eula
line in the vernemq.conf
file from no
to yes
or accepting the EULA the first time starting VerneMQ. In general, the installation of VerneMQ OS packages is now a 3 step process:
If you install the package with tools like dpkg
(example: sudo dpkg -i vernemq-1.10.0.xenial.x86_64.deb
), VerneMQ will install but will fail to start due to the missing EULA acceptance.
Accept the EULA by running sudo vernemq chkconfig
or by adding the following line to your vernemq.conf file
: accept_eula = yes
.
Start/restart VerneMQ with: sudo systemctl restart vernemq.
For Docker images the EULA can be accepted by setting the environment variableDOCKER_VERNEMQ_ACCEPT_EULA=yes
, for Docker Swarm add DOCKER_VERNEMQ_ACCEPT_EULA: yes
to the environment.
For the Helm chart the EULA for the Docker images can be accepted by extending the additionalEnv
section with:
additionalEnv:
- name: DOCKER_VERNEMQ_ACCEPT_EULA
value: "yes"
and similarly for the VerneMQ Operator, to accept the EULA for the Docker images, the env
can be extended with:
env:
- name: DOCKER_VERNEMQ_ACCEPT_EULA
value: "yes"
VerneMQ can be installed on CentOS-based systems using the binary package we provide.
Once you have downloaded the binary package, execute the following command to install VerneMQ:
or:
To use the provided binary packages the VerneMQ EULA must be accepted. See Accepting the VerneMQ EULA for more information.
Once you've installed VerneMQ, start it on your node:
You can verify that VerneMQ is successfully installed by running:
If VerneMQ has been installed successfully vernemq
is returned.
Now that you've installed VerneMQ, check out How to configure VerneMQ.
VerneMQ can be installed on Debian or Ubuntu-based systems using the binary package we provide.
Once you have downloaded the binary package, execute the following command to install VerneMQ:
You can verify that VerneMQ is successfully installed by running:
If VerneMQ has been installed successfully Status: install ok installed
is returned.
To use the provided binary packages the VerneMQ EULA must be accepted. See Accepting the VerneMQ EULA for more information.
Once you've installed VerneMQ, start it on your node:
The whereis vernemq
command will give you a couple of directories:
Path
Description
/usr/sbin/vernemq:
the vernemq and vmq-admin commands
/usr/lib/vernemq
the vernemq package
/etc/vernemq
the vernemq.conf file
/usr/share/vernemq
the internal vernemq schema files
/var/lib/vernemq
the vernemq data dirs for LevelDB (Metadata Store and Message Store)
Now that you've installed VerneMQ, check out How to configure VerneMQ.
Set the maximum size for client ids, MQTT v3.1 specifies a limit of 23 characters.
This option default to 23
.
This option allows persistent clients (those with clean_session
set to false
) to be removed if they do not reconnect within a certain time frame.
This is a non-standard option. As far as the MQTT specification is concerned, persistent clients are persisted forever.
The expiration period should be an integer followed by one of h
, d
, w
, m
, y
for hour, day, week, month, and year; or never
:
This option defaults to never
.
Limit the maximum publish payload size in bytes that VerneMQ allows. Messages that exceed this size won't be accepted.
Defaults to 0
, which means that all valid messages are accepted. MQTT specification imposes a maximum payload size of 268435455 bytes.
VerneMQ supports multiple ways to configure one or many MQTT listeners.
Listeners specify on which IP address and port VerneMQ should accept new incoming connections. Depending on the chosen transport (TCP, SSL, WebSocket) different configuration parameters have to be provided. VerneMQ allows to write the listener configurations in a hierarchical manner, enabling very flexible setups. VerneMQ applies reasonable defaults on the top level, which can be of course overridden if needed.
These are the only default parameters that are applied for all transports, and the only one that are of interest for plain TCP and WebSocket listeners.
These global defaults can be overridden for a specific transport protocol listener.tcp.CONFIG = VAL
, or even for a specific listener listener.tcp.LISTENER.CONFIG = VAL
. The placeholder LISTENER
is freely chosen and is only used as a reference for further configuring this particular listener.
Normally, an MQTT broker hosts one single topic tree. This means that all topics are accessible to all publishers and subscribers (limited by the ACLs you configured, of course). Mountpoints are a way to host multiple topic trees in a single broker. They are completely separated and clients with different topic trees cannot publish messages to each other. This could be useful if you provide MQTT services to multiple separated use cases/verticals or clients, with a single broker. Note that mountpoints are configured via different listeners. As a consequence, the MQTT clients will have to connect to a specific port to connect to a specific topic space (mountpoint).
The mountpoints can be configured on the protocol level or configurred or overridden on the specific listener level.
Since VerneMQ 1.5.0 it is possible to configure which MQTT protocol versions as listener will accept.
VerneMQ supports MQTT 3.1, 3.1.1, and 5.0 (since VerneMQ 1.6.0). To allow these protocol versions, set:
Here 3,4,5
are the protocol level versions corresponding to MQTT 3.1, 3.1.1 and 5.0 respectively. The default value is 3,4
thus allowing MQTT 3.1 and 3.1.1, while MQTT 5.0 is disabled.
Listen on TCP port 1883 and for WebSocket Connections on port 8888:
An additional listener can be added by using a different name. In the example above the name equals to default
and can be used for further configuring this particular listener. The following example demonstrates how an additional listener is defined as well as how the maximum number of connections can be limited for this listener:
VerneMQ listeners can be configured to accept connections from a proxy server that supports the PROXY protocol. This enables VerneMQ to retrieve peer information such as source IP/Port but also PROXY Version 2 protocol TLS client certificate details if the proxy was used to terminate TLS.
To enable the PROXY protocol for tcp listeners use listener.tcp.proxy_protocol = on
or for a specific listener use listener.tcp.LISTENER.proxy_protocol = on
.
If client certificates are used you can set listener.tcp.proxy_protocol_use_cn_as_username = on
which will overwrite the MQTT username set by the client with the common name from the client certificate before authentication and authorization is performed.
Accepting SSL connections on port 8883:
If you want to use client certificates to authenticate your clients you have to set the following option:
If you use client certificates and want to use the certificates CN value as a username you can set:
Both options require_certificate
and use_identity_as_username
default to off
.
The same configuration options can be used for securing WebSocket connections, just use wss
as the protocol identifier e.g. listener.wss.require_certificate
.
With SSL, you still need to configure authentication and authorization! That is, set allow_anonymous
to off
, and configure vmq_acl and vmq_passwd or your authentication plugin.
The default listener listener.vmq.clustering
is used for distributing MQTT messages among the cluster nodes.
VerneMQ supports multiple ways to authenticate and authorize new client connections using a database.
VerneMQ supports authentication and authorization using a number of popular databases and the below sections describe how to configure the different databases.
The database drivers are handled using the vmq_diversity
plugin and it therefore needs to be enabled:
The vmq_diversity
plugin makes it possible to extend VerneMQ using Lua. The documentation can be found here.
When using database based authentication/authorization the enabled-by-default file based authentication and authorization are most likely not needed and should be disabled:
You must set allow_anonymous = off
, otherwise VerneMQ won't use the database plugin for authentication and authorization.
In order to use a database for authentication and authorization the database must be properly configured and the auth-data (username, clientid, password, acls) to be present. The following sections show some sample requests that can be used to insert such data.
While the handling of authentication differs among the different databases, the handling of ACLs is roughly identical and make use of a JSON array containing one or many ACL objects per configured client.
The database integrations will cache the ACLs when the client connects avoiding expensive database lookups for each publish or subscribe message. The cache entries are evicted when the client disconnects.
A minimal publish & subscribe ACL JSON object takes the following form:
General ACL
The pattern is a MQTT topic string that can contain MQTT wildcards, but also the template variables %m
(mountpoint), %u
(username), and %c
(client id) which are automatically substituted with the auth data provided.
Publish ACL
The publish ACL makes it possible to control the maximum QoS and payload size that is allowed, and if the message is allowed to be retained.
Moreover, the publish ACL makes it possible to modify the properties of a published message through specifying one or multiple modifiers
. Please note that the modified message isn't re-validated by the ACL.
Subscribe ACL
The subscribe ACL makes it possible to control the maxium QoS a client is allowed to subscribe to.
Like the publish ACL, the subscribe ACL makes it possible to change the current subscription request by returning a custom set of topic/qos pairs. Please note that the modified subscription isn't re-validated by the ACL.
When deciding on which database to use one has to consider which kind of password hashing and key derivation functions are available and required. Different databases provide different mechanisms, for example PostgreSQL provides the pgcrypto
module which supports verifying hashed and salted passwords, while Redis has no such features. VerneMQ therefore also provides client-side password verification mechanisms such as bcrypt
.
There is a trade-off between verifying passwords on the client-side versus on the server-side. Verifying passwords client-side of course means doing the computations on the VerneMQ broker and this takes away resources from other tasks such as routing messages. With hashing functions such as bcrypt
which are designed specifically to be slow (proportional to the number of rounds) in order to make brute-force attacks infeasible, this can become a problem. For example, if verifying a password with bcrypt
takes 0.5 seconds then on a single threaded core 2 verifications/second are possible and using 4 single threaded cores 8 verifications/second. So, the number of rounds/security paramenters have a direct impact on the max number of verifications/second and hence also the maximum arrival rate of new clients per second.
For each database it is specified which password verification mechanisms are available and if they are client-side or server-side.
To enable PostgreSQL authentication and authorization the following need to be configured in the vernemq.conf
file:
PostgreSQL hashing methods:
method
client-side
server-side
bcrypt
✓
crypt
✓
The following SQL DDL must be applied, the pgcrypto
extension is required if using the server-side crypt
hashing method:
To enter new ACL entries use a query similar to the following:
To enable CockroachDB authentication and authorization the following need to be configured in the vernemq.conf
file:
Notice that if the CockroachDB installation is secure, then TLS is required. If using an insecure installation without TLS, then vmq_diversity.cockroachdb.ssl
can be set to off
.
CockroachDB hashing methods:
method
client-side
server-side
bcrypt
✓
sha256
✓
The following SQL DDL must be applied:
To enter new ACL entries use a query similar to the following, the example is for the bcrypt
hashing method:
For MySQL authentication and authorization configure the following in vernemq.conf
:
MySQL hashing methods:
method
client-side
server-side
sha256
✓
md5*
✓
sha1*
✓
password
✓
It should be noted that all the above options stores unsalted passwords which are vulnerable to rainbow table attacks, so the threat-model should be considered carefully when using these. Also note the methods marked with *
are no longer considered secure hashes.
The following SQL DDL must be applied:
To enter new ACL entries use a query similar to the following, the example uses PASSWWORD
to for password hashing:
Note, the PASSWORD()
hashing method needs to be changed according to the configuration set in vmq_diversity.mysql.password_hash_method
, it supports the options password
, md5
, sha1
and sha256
. Learn more about the MySQL equivalent for those methods on https://dev.mysql.com/doc/refman/8.0/en/encryption-functions.html.
The default password
method has been deprecated since MySQL 5.7.6 and not usable with MySQL 8.0.11+. Also, the MySQL authentication method caching_sha2_password
is not supported. This is the default in MySQL 8.0.4 and later, so you need to add: default_authentication_plugin=mysql_native_password
under [mysqld] in e.g. /etc/mysql/my.cnf.
For MongoDB authentication and authorization configure the following in vernemq.conf
:
MongoDB hashing methods:
method
client-side
server-side
bcrypt
✓
Insert the ACL using the mongo
shell or any software library. The passhash
property contains the bcrypt hash of the clients password.
For Redis authentication and authorization configure the following in vernemq.conf
:
Redis hashing methods:
method
client-side
server-side
bcrypt
✓
Insert the ACL using the redis-cli
shell or any software library. The passhash
property contains the bcrypt hash of the clients password. The key is an encoded JSON array containing the mountpoint, username, and client id. Note that no spaces are allowed between the array items.
Note, currently bcrypt version 2a
(prefix $2a$
) is supported.
How to setup and configure the HTTP listener.
The VerneMQ HTTP listener is used to serve various VerneMQ subsystems such as:
By default it runs on port 8888
. To disable the HTTP listener or change the port, adapt the configuration in vernemq.conf
:
Where should VerneMQ emit the default console log messages (which are typically at info
severity):
VerneMQ defaults to log the console messages to a file, which can specified by:
This option defaults to /var/log/vernemq/console.log
for Ubuntu, Debian, RHEL and Docker installs.
The default console logging level info
could be setting one of the following:
VerneMQ log error messages by default. One can change the default behaviour by setting:
VerneMQ defaults to log the error messages to a file, which can specified by:
This option defaults to /var/log/vernemq/error.log
for Ubuntu, Debian, RHEL and Docker installs.
VerneMQ log crash messages by default. One can change the default behaviour by setting:
VerneMQ defaults to log the crash messages to a file, which can specified by:
This option defaults to /var/log/vernemq/crash.log
for Ubuntu, Debian, RHEL and Docker installs.
The maximum sizes in bytes of inidividual messages in the crash log defaults to 64KB
but can be specified by:
VerneMQ rotate crash logs. By default, the crash log file is rotated at midnight or when the size exceeds 10MGB
. This behaviour can be changed by setting:
The default number of rotated log files is 5 and can be set with the option:
VerneMQ supports logging to SysLog, enable it by setting:
Logging to SysLog is disabled by default.
Many aspects of VerneMQ can be extended using plugins. The standard VerneMQ package comes with several official plugins. You can show the enabled & running plugins via:
The command above displays all the enabled plugins together with the hooks they implement:
This enables the ACL plugin. Because the vmq_acl
plugin is already started the above command won't succeed. In case the plugin sits in an external directory you must also to provide the --path=PathToPlugin
.
To make a plugin start when VerneMQ starts they need to be configured in the main vernemq.conf
file.
The general syntax to enable a plugin is to add a line like plugins.pluginname = on
, using the vmq_passwd
plugin as an example:
And if the plugin is external the path can be specified like this:
Plugin specific settings can be configured via myplugin.somesetting = value
, like:
See the vernemq.conf
file for details.
Set the time in seconds after a QoS=1 or QoS=2
message has been sent that VerneMQ will wait before retrying when no response is received.
This option default to 20
seconds.
This option defines the maximum number of QoS 1 or 2 messages that can be in the process of being transmitted simultaneously.
Defaults to 20
messages, use 0
for no limit. The inflight window serves as a protection for sessions, on the incoming side.
The maximum number of messages to hold in the queue above those messages that are currently in flight. Defaults to 1000
. Set to -1
for no limit. This option protects a client session from overload by dropping messages (of any QoS).
Defaults to 1000
messages, use -1
for no limit. This parameter was named max_queued_messages
in 0.10.*
. Note that 0
will totally block message delivery from any queue!
This option specifies the maximum number of QoS 1 and 2 messages to hold in the offline queue.
Defaults to 1000
messages, use -1
for no limit, use 0
if no messages should be stored.
In contrast to the session based inflight window, max_online_messages and max_offline_messages serves as a protection of queues, on the outgoing side.
There are a couple of hidden options you can set in the vernemq.conf
file. Hidden means that you have to add and set the value explicitly. Hidden options still have default values. Changing them should be considered advanced, possibly with the exception of setting a max_message_rate
.
Specify how the queue should deliver messages when multiple sessions are allowed. In case of fanout
all the attached sessions will receive the message, in case of balance
an attached session is choosen randomly.
Specify how queues should process messages, either the fifo
or lifo
way. Default is fifo
.
Specifies the maximum incoming publish rate per session per second. Depending on the underlying network buffers this rate isn't enforced. Defaults to 0
, which means no rate limits apply. Setting to a value of 2
limits any publisher to 2 messages per second, for instance.
Due to the eventual consistent nature of the subscriber store it is possible that during queue migration messages still arrive on the old cluster node. This parameter enables to compensate this by keeping the queue around for some time (in seconds) after it was migrated to the other cluster node.
Specifies the number of messages that are delivered to the remote node per drain step. A large value will provide a faster migration of a queue, but increases the waste of bandwidth in case the migration fails.
Allows to select a new default reg_view. A reg_view is a pre-defined way to route messages. Multiple views can be loaded and used, but one has to be selected as a default. The default routing is vmq_reg_trie
, i.e. routing via the built-in trie data structure.
A list of views that are started during startup. It's only used in plugins that want to choose dynamically between routing reg_views.
An integer specifying how many bytes are buffered in case the remote node is not available. Default is 10000
VerneMQ supports the WebSocket protocol out of the box. To be able to open a WebSocket connection to VerneMQ, you have to configure a WebSocket listener or Secure WebSocket listener in the vernemq.conf
file first:
Keep in mind that you'll use MQTT-over-WebSocket, so you will need a Javascript library that implements the MQTT client behaviour. We have used the as well as
You won't be able to open WebSocket connections on a base URL, always add the /mqtt
path.
Consumer session balancing has been deprecated and will be removed in VerneMQ 2.0. Use instead.
Sometimes consumers get overwhelmed by the number of messages they receive. VerneMQ can load balance between multiple consumer instances subscribed to the same topic with the same ClientId.
To enable session balancing, activate the following two settings in vernemq.conf
Currently those settings will activate consumer session balancing globally on the respective node. Restricting balancing to specific consumers only, will require a plugin. Note that you cannot balance consumers spread over different cluster nodes.
Working with shared subscriptions
A shared subscription is a mechanism for distributing messages to a set of subscribers to shared subscription topic, such that each message is received by only one subscriber. This contrasts with normal subscriptions where each subscriber will receive a copy of the published message.
A shared subscription is on the form $share/sharename/topic
and subscribers to this topic will receive messages published to the topic topic
. The messages will be distributed according to the defined distribution policy.
When subscribing to a shared subscription using command line tools remember to quote the topic as some command line shells, like bash
, will otherwise expand the $share
part of the topic as an environment variable.
Currently three message distribution policies for shared subscriptions are supported: prefer_local
, random
and local_only
. Under the random
policy messages will be published to a random member of the shared subscription, if any exist. Under the prefer_local
policy messages will be delivered to a random node-local member of the shared subscription, if none exist, the message will be delivered to a random member of the shared subscription on a remote cluster node. Under the local_only
policy message will be delivered to a random node-local member of the shared subscription.
When a messages is being delivered to subscribers of a shared subscription, the message will be delivered to an online subscriber if possible, otherwise the message will be delivered to an offline subscriber.
Note that Shared Subscriptions still fully operate under the MQTT specification (be it MQTT 5.0 or backported to older protocol versions). Be aware of this, especially regarding QoS and clean_session configurations.
Subscriptions Note: When subscribing to a shared topic, make sure to escape the $
So, for dash or bash shells
Publishing Note: When publishing to a shared topic, do not include the prefix $share/group/
as part of the publish topic name
On every VerneMQ node you'll find the vmq-admin
command line tool in the release's bin directory. It has different sub-commands that let you check for status, start and stop listeners, re-configure values and a couple of other administrative tasks.
vmq-admin
works by RPC'ing into the local VerneMQ node by default. For most commands you can add a --node
option and set values on other cluster nodes, even if the local VerneMQ node is down.
To check for the global cluster state in case the local VerneMQ node is down, you'll have to go to another node though.
vmq-admin
is a live re-configuration utility. Please note that all dynamically configured values will be reset by vernemq.conf upon broker restart.
Don't use this to wildly re-configure a production system without keeping track what you are doing. vmq-admin
gives you the flexibility to test stuff and react live, but please persistent any static configuration you need in the vernemq.conf file.
VerneMQ uses the Erlang distribution mechanism for most inter-node communication. VerneMQ identifies other machines in the cluster using Erlang identifiers (e.g. VerneMQ@10.9.8.7
). Erlang resolves these node identifiers to a TCP port on a given machine via the Erlang Port Mapper daemon (epmd) running on each cluster node.
By default, epmd binds to TCP port 4369 and listens on the wildcard interface. For inter-node communication, Erlang uses an unpredictable port by default; it binds to port 0, which means the first available port.
For ease of firewall configuration, VerneMQ can be configured to instruct the Erlang interpreter to use a limited range of ports. For example, to restrict the range of ports that Erlang will use for inter-Erlang node communication to 6000-7999, add the following lines to vernemq.conf on each VerneMQ node:
The settings above are only used for distributing subscription updates and maintenance messages. For distributing the 'real' MQTT messages the proper vmq
listener must be configured in the vernemq.conf.
It isn't necessary to configure the same port on every machine, as the nodes will probe each other for this information.
Attributions:
This section, "VerneMQ Inter-node Communication", is a derivative of Security and Firewalls by Riak, used under Creative Commons Attribution 3.0 Unported License.
Bridges are a non-standard way, although kind of a de-facto standard among MQTT broker implementations, to connect two different MQTT brokers to eachother. This allows for example that a topic tree of a remote broker becomes part of the topic tree on the local broker. VerneMQ supports plain TCP connections as well as SSL connections.
in VerneMQ the bridge is distributed with VerneMQ as a plugin and is not enabled by default. After configuring the bridge as described below, make sure to enable the plugin by setting:
See Managing plugins for more information on working with plugins.
When the plugin is enabled a simple status interface is available:
Setup a bridge to a remote broker:
Different connection parameters can be set:
Define the topics the bridge should incorporate in its local topic tree (by subscribing to the remote), or the topics it should export to the remote broker (by publishing to the remote). We share a similar configuration syntax to that used by the Mosquitto broker:
topic
defines a topic pattern that is shared between the two brokers. Any topics matching the pattern (which may include wildcards) are shared. The second parameter defines the direction that the messages will be shared in, so it is possible to import messages from a remote broker usingin
, export messages to a remote broker usingout
or share messages inboth
directions. If this parameter is not defined, VerneMQ defaults toout
. The QoS level defines the publish/subscribe QoS level used for this topic and defaults to0
. (Source: mosquitto.conf)
The local-prefix
and remote-prefix
can be used to prefix incoming or outgoing publish messages.
Currently the #
wildcard is treated as a comment from the configuration parser, please use *
instead.
A simple example:
SSL bridges support the same configuration parameters as TCP bridges, but need further instructions for handling the SSL specifics:
VerneMQ can be easily clustered. Clients can then connect to any cluster node and receive messages from any other cluster nodes. However, the MQTT specification gives certain guarantees that are hard to fulfill in a distributed environment, especially when network partitions occur. We'll discuss the way VerneMQ deals with network partitions in its own subsection
Set the Cookie! All cluster nodes need to be configured to use the same Cookie value. It can be set in the vernemq.conf
with the distributed_cookie
setting. Set the Cookie to a private value for security reasons!
For a successful VerneMQ cluster setup, it is important to choose proper VerneMQ node names. In vernemq.conf
change the nodename = VerneMQ@127.0.0.1
to something appropriate. Make sure that the node names are unique within the cluster. Read the section on VerneMQ Inter-node Communication if firewalls are involved.
Before you go ahead and experience the full power of clustering VerneMQ, be aware of its stateful character. An MQTT broker is a stateful application and a VerneMQ cluster is a stateful cluster.
What does this mean in detail? It means that clustered VerneMQ nodes will share information about connected clients and sessions but also meta-information about the cluster itself.
For instance, if you stop a cluster node, the VerneMQ cluster will not just forget about it. It will know that there's a node missing and it will keep looking for it. It will know there's a netsplit situation and it will heal the partition when the node comes back up. But if the missing nodes never comes back there's an eternal netsplit. (still resolvable by making the missing nodes explicitly leave).
This doesn't mean that a VerneMQ cluster cannot dynamically grow and shrink. But it means you have to tell the cluster what you intend to do, by using join and leave commands.
If you want a cluster node to leave the cluster, well... use the vmq-admin cluster leave
command. If you want a node to join a cluster, well... use the vmq-admin cluster join
command.
Makes sense? Go ahead and create your first VerneMQ cluster!
A cluster leave will actually do a lot more work, and gives you some options to choose. The node leaving the cluster will go to great length trying to migrate its existing queues to other nodes. As queues (online or offline) are live processes in a VerneMQ node, it will only exit after it has migrated them.
Let's look at the steps in detail:
vmq-admin cluster leave node=<NodeThatShouldGo>
This first step will only stop the MQTT Listeners of the node to ensure that no new connections are accepted. It will not interrupt the existing connections, and behind the scenes the node will not leave the cluster yet. Existing clients are still able to publish and receive messages at this point.
The idea is to give a grace period with the hope that existing clients might re-connect (to another node). If you have decided that this period is over (after 5 minutes or 1 day is up to you), you proceed with step 2: disconnecting the rest of the clients.
vmq-admin cluster leave node=<NodeThatShouldGo> -k
The -k
flag will delete the MQTT Listeners of the leaving node, taking down all live connections. If this is what you want from the beginning, you can do this right away as a first step.
Now, queue migration is triggered by clients re-connecting to other nodes. They will claim their queue and it will get migrated. Still, there might be some offline queues remaining on the leaving node, because they were pre-existing or because some clients do not re-connect and do not reclaim their queues.
VerneMQ will throw an exception if there are remaining offline queues after a configurable timeout. The default is 60 seconds, but you can set it as an option to the cluster leave command. As soon as the exception shows in console or console.log, you can actually retry the cluster leave command (including setting a migration timeout (-t
), and an interval in seconds (-i
) indicating how often information on the migration progress should be printed to the console.log):
vmq-admin cluster leave node=<NodeThatShouldGo> -k -i 5 -t 120
After this timeout VerneMQ will forcefully migrate the remaining offline queues to other cluster nodes in a round robin manner. After doing that, it will stop the leaving VerneMQ node.
Note 1: While doing a cluster leave, it's a good idea to tail -f the VerneMQ console.log to see queue migration progress.
Note 2: A node that has left the cluster is considered dead. If you want to reuse that node as a single node broker, you have to (backup & rename &) delete the whole VerneMQdata
directory and start with a new directory. (It will be created automatically by VerneMQ at boot).
Otherwise that node will start looking for its old cluster peers when you restart it.
So, case A was the happy case. You left the cluster with your node in a controlled manner, and everything worked, including a complete queue (and message) transfer to other nodes.
Let's look at the second possibility where the node is already down. Your cluster is still counting on it though and possibly blocking new subscription for that reason, so you want to make the node leave.
To do this, use the same command(s) as in the first case. There is one important consequence to note: by making a stopped node leave, you basically throw away persistant queue content, as VerneMQ won't be able to migrate or deliver it.
Let's repeat that to make sure:
Case B: Currently the persisted QoS 1 & QoS 2 messages aren't replicated to the other nodes by the default message store backend. Currently you will lose the offline messages stored on the leaving node.
This section elaborates how a VerneMQ cluster deals with network partitions (aka. netsplit or split brain situation). A netsplit is mostly the result of a failure of one or more network devices resulting in a cluster where nodes can no longer reach each other.
VerneMQ is able to detect a network partition, and by default it will stop serving CONNECT
, PUBLISH
, SUBSCRIBE
, and UNSUBSCRIBE
requests. A properly implemented client will always resend unacked commands and messages are therefore not lost (QoS 0 publishes will be lost). However, the time window between the network partition and the time VerneMQ detects the partition much can happen. Moreover, this time frame will be different on every participating cluster node. In this guide we're referring to this time frame as the Window of Uncertainty.
The behaviour during a netsplit is completely configurable via allow_register_during_netsplit
, allow_publish_during_netsplit
, allow_subscribe_during_netsplit
, and allow_unsubscribe_during_netsplit
. These options supersede the trade_consistency
option. In order to reach the same behaviour as trade_consistency = on
all the mentioned netsplit options have to set to on
.
VerneMQ follows an eventually consistent model for storing and replicating the subscription data. This also includes retained messages.
Due to the eventually consistent data model it is possible that during the Window of Uncertainty a publish won't take into account a subscription made on a remote node (in another partition). Obviously, VerneMQ can't deliver the message in this case. The same holds for delivering retained messages to remote subscribers.
last will
messages that are triggered during the Window of Uncertainty will be delivered to the reachable subscribers. Currently during a netsplit, but after the Window of Uncertainty last will messages will be lost.
Normally, client registration is synchronized using an elected leader node for the given client id. Such a synchronization removes the race condition between multiple clients trying to connect with the same client id on different nodes. However, during the Window of Uncertainty it is currently possible that VerneMQ fails to disconnect a client connected to a different node. Although this scenario sounds like artificially crafted it is possible to end up with duplicate clients connected to the cluster.
As soon as the partition is healed, and connectivity reestablished, the VerneMQ nodes replicate the latest changes made to the subscription data. This includes all the changes 'accidentally' made during the Window of Uncertainty. Using Dotted Version Vectors VerneMQ ensures that convergence regarding subscription data and retained messages is eventually reached.
VerneMQ uses Google's LevelDB as a fast storage backend for messages and subscriber information. Each VerneMQ node runs its own embedded LevelDB store.
There's not much you need to know about LevelDB and VerneMQ. One really important thing to note is that LevelDB manages its own memory. This means that VerneMQ will not allocate and free memory for LevelDB. Instead you'll have to configure a configuration value in vernemq.conf that tells LevelDB how much memory it can use up.
Configuring LevelDB memory:
LevelDB means business with its allocated memory. It will eventually end up with the configured max, making it look like there's a memory leak, or even triggering OOM kills. Keep that in mind when configuring the percentage of RAM you give to LevelDB.
You can dynamically re-configure most of VerneMQ's settings on a running node by using the vmq-admin set
command.
The following config values can be handled dynamically:
Settings dynamically configured with the vmq-admin set
command will be reset by vernemq.conf upon broker restart.
Let's change the max_client_id_size
as an example. (We might have noticed that some clients can't login because their client ID is too long, but we don't want to restart the broker for that). Note that you can also set multiple values with the same command.
You can show one or multiple values in a simple table:
Inspecting and managing MQTT sessions
VerneMQ comes with powerful tools for inspecting the state of MQTT sessions. To list current MQTT sessions simply invoke vmq-admin session show
:
To see detailed information about the command see vmq-admin session show --help
.
The command is able to show a lot of different information about a client, for example the client id, the peer host and port if the client is online or offline and much more, see vmq-admin session show --help
for details. Further the information can also be used to filter information which is very helpful when wanting to narrow down the information to a single client.
A sample query which lists only the node where the client session exists and if the client is online would look like the following:
Note, by default a maximum of 100 rows are returned from each node in the cluster. This is a mechanism to protect the cluster from overload as there can be millions of MQTT sessions and resulting rows. Use --limit=<RowLimit>
to override the default value.
Listing the clients and the subscriptions one can do the following:
And to list only the clients subscribed to the topic some/topic
:
To figure out when the queue for a persisted session (clean_session=false) was created and when the client last connected one can use the --queue_started_at
and --session_started_at
to list the POSIX timestamps (in microseconds):
Besides the examples above it is also possible to inspect the number of online or offline messages as well as their payloads and much more. See vmq-admin session show --help
for an exhaustive list of all the available options.
VerneMQ also supports disconnecting clients and reauthorizing client subscriptions. To disconnect a client and cleanup store messages and remove subscriptions one can invoke:
See vmq-admin session disconnect --help
for more options and details.
To reauthorize subscriptions for a client issue the following command:
This works by reapplying the logic in any installed auth_on_subscribe
or auth_on_subscribe_m5
plugin hooks to check the validity of the existing topics and removing those that are no longer allowed. In the example above the reauthorization of the client subscriptions resulted in no changes.
You can configure as many listeners as you wish in the vernemq.conf file. In addition to this, the vmq-admin listener
command let's you configure, start, stop and delete listeners on the fly. Those can be MQTT, WebSocket or Cluster listeners, in the command line output they will be tagged mqtt, ws or vmq accordingly.
To get info on a listener sub-command, invoke it with the --help option. Example: vmq-admin listener start --help
Listeners configured with the vmq-admin listener
command will not survive a broker restart. Live changes to listeners configured in vernemq.conf are possible, but the vernemq.conf listeners will just be restarted with a broker restart.
This will start an MQTT listener on port 1884
and IP address 192.168.1.50
. If you want to start a WebSocket listener, just tell VerneMQ by adding the --websocket
flag. There are more options, mainly for configuring SSL (use vmq-admin listener start --help
).
You can isolate client connections accepted by a certain listener from other clients by setting a mountpoint.
To start an MQTT listener using defaults, just set the port and IP address as a minimum.
You can add the -k
or --kill_sessions
switch to that command. This will disconnect all client connections setup by that listener. In combination with a mountpoint, this can be useful for terminating clients for a specific application, or to force re-connects to another cluster node (to prepare for a cluster leave for your node).
Inspecting the retained message store
To list the retained messages simply invoke vmq-admin retain show
:
Note, by default a maximum of 100 results are returned. This is a mechanism to protect the from overload as there can be millions of retained messages. Use --limit=<RowLimit>
to override the default value.
Besides listing the retained messages it is also possible to filter them:
In the above example we list only the payload for the topic some/topic
.
Another example where all topics are list with retained messages with a specific payload:
See the full set of options and documentation by invoking vmq-admin retain show --help
.
Everything you need to know to work with the VerneMQ HTTP administration interface
The VerneMQ HTTP API is enabled by default and installs an HTTP handler on http://localhost:8888/api/v1
. To read more about configuring the HTTP listener, see HTTP Listener Configuration. You can configure a HTTP listener, or a HTTPS listener to serve the HTTP API v1.
The VerneMQ HTTP API uses basic authentication where an API key is passed as the username and the password is left empty. So the first step to us the HTTP API is to create an API key:
The key is persisted and available on all cluster nodes.
To list existing keys do:
To add an API key of your own choosing, do:
To delete an API key do:
The VerneMQ HTTP API is a wrapper over the vmq-admin
CLI tool, and anything that can be done using vmq-admin
can be done using the HTTP API. Note that the HTTP API is therefore subject to any changes made to the vmq-admin
tools and their flags & options structure. All requests are performed doing a HTTP GET and if no errors occurred an HTTP 200 OK code is returned with a possible non-empty JSON payload.
The API is using basic auth where the API key is passed as the username. An example using curl
would look like this:
The mapping between vmq-admin
and the HTTP API is straightforward, and if one is already familiar with how the vmq-admin
tool works, working with the API should be easy. The mapping works such that the command part of a vmq-admin
invocation is turned into a path, and the options and flags are turned into the query string.
A mandatory parameter like the client-id
in the vmq-admin session disconnect client-id=myclient
command should be translated as: ?client-id=myclient
.
An optional flag like --cleanup
in the vmq-admin session disconnect client-id=myclient --cleanup
command should be translated as: &--cleanup
Let's look at the cluster join command as an example, which looks like this:
This turns into a GET request:
To test, run it with curl
:
And the returned response would look like:
Below are some other examples.
Request:
Curl:
Response:
Request:
Curl:
Response:
Request:
Curl:
Response:
Request:
Curl:
Response:
Request:
Curl:
Response:
Request:
Curl:
Response:
When working with a system like VerneMQ sometimes when troubleshooting it would be nice to know what a client is actually sending and receiving and what VerneMQ is doing with this information. For this purpose VerneMQ has a built-in tracing mechanism which is safe to use in production settings as there is very little overhead in running the tracer and has built-in protection mechanisms to stop traces that produce too much information.
To trace a client the following command is available:
See the available flags by calling vmq-admin trace client --help
.
A typical trace could look like the following:
In this particular trace a trace was started for the client with client-id client
. At first no clients are connected to the node where the trace has been started, but a little later the client connects and we see the trace come alive. The strange identifier <7616.3443.1>
is called a process identifier and is the identifier of the process in which the trace happened - this isn't relevant unless one wants to correlate the trace with log entries where process identifiers are also logged. Besides the process identifier there are some lines with MQTT SEND
and MQTT RECV
which are to be understood from the perspective of the broker. In the above trace this means that first the broker receives a CONNECT
frame and replies with a CONNACK
frame. Each MQTT event is annotated with the data from the MQTT frame to give as much detail and insight as possible.
Notice the auth_on_register
call between CONNECT
and CONNACK
which is the authentication plugin hook being called to authenticate the client. In this case the hook returned ok
which means the client was successfully authenticated.
Likewise notice the auth_on_subscribe
call between the SUBSCRIBE
and SUBACK
frames which is plugin hook used to authorize if this particular subscription should be allowed or not. In this case the subscription was authorized.
A convenient tool is the ts
(timestamp) tool which is available on many systems. If the trace output is piped to this command each line is prefixed with a timestamp.
The VerneMQ status page
VerneMQ comes with a built-in status page which by default is enabled and is available on http://localhost:8888/status
, see HTTP listeners.
The status page is a simple overview of the cluster and the individual nodes in the cluster as seen below:
The VerneMQ health checker
A simple way to gauge the health of a VerneMQ cluster is to query the /health
path on the .
The health check will return 200 when VerneMQ is accepting connections and is joined with the cluster (for clustered setups). 503 will be returned in case any of those two conditions are not met.
The graphite exporter reports the broker metrics at a fixed interval (defined in milliseconds) to a graphite server. The necessary configuration is done inside the vernemq.conf
.
You can further tune the connection to the Graphite server:
The above configuration parameters can be changed at runtime using the vmq-admin
script.
Usage: vmq-admin set = ... [[--node | -n] | --all]
Example: vmq-admin set graphite_interval=20000 graphite_port=2003 -n VerneMQ@127.0.0.1
Description and Configuration of the built-in Monitoring mechanism
VerneMQ can be monitored in several ways. We implemented native support for , , and .
The metrics are also available via the command line tool:
Or with:
Which will output the metrics together with a short description describing what the metric is about. An example looks like:
Notice that the metrics:
Are no longer used (always 0) and will be removed in the future. They were replaced with mqtt_connack_sent
using the return_code
label. For MQTT 5.0 the reason_code
label is used instead.
The output on the command line are aggregated by default, but details for a label can be shown as well, for example all metrics with the not_authorized
label:
All available labels can be show using vmq-admin metrics show --help
.
In this section the publish flow is described. VerneMQ provides multiple hooks throughout the flow of a message. The most important ones are the auth_on_publish
and auth_on_publish_m5
hooks which acts as an application level firewall granting or rejecting a publish message.
Every plugin that implements the auth_on_publish
or auth_on_publish_m5
hooks are part of a conditional plugin chain. For this reason we allow the hook to return different values. In case the plugin can't validate the publish message it is best to return next
as this would allow subsequent plugins in the chain to validate the request. If no plugin is able to validate the request it gets automatically rejected.
Every plugin that implements the on_deliver
or on_deliver_m5
hooks are part of a conditional plugin chain, although NO verdict is required in this case. The message gets delivered in any case. If your plugin uses this hook to rewrite the message the plugin system stops evaluating subsequent plugins in the chain.
VerneMQ provides multiple hooks throughout the lifetime of a session. The most important ones are the auth_on_register
and auth_on_register_m5
hooks which act as an application level firewall granting or rejecting new clients.
Every plugin that implements the auth_on_register
or auth_on_register_m5
hooks are part of a conditional plugin chain. For this reason we allow the hook to return different values depending on how the plugin grants or rejects this client. In case the plugin doesn't know the client it is best to return next
as this would allow subsequent plugins in the chain to validate this client. If no plugin is able to validate the client it gets automatically rejected.
The systree functionality is enabled by default and reports the broker metrics at a fixed interval defined in the vernemq.conf
. The metrics defined are transformed to MQTT topics e.g. mqtt_publish_received
is transformed to $SYS/<nodename>/mqtt/publish/received
. <nodename>
is your node's name, as configured in the vernemq.conf
. To find it, you can grep the file for it: grep nodename vernemq.conf
The complete list of metrics can be found
This option defaults to 20000
milliseconds.
If the systree feature is not required it can be disabled in vernemq.conf
The feature and the interval can be changed at runtime using the vmq-admin
script.
Usage: vmq-admin set = ... [[--node | -n] | --all]
Example: vmq-admin set systree_interval=60000 -n VerneMQ@127.0.0.1
Examples:
VerneMQ is implemented in Erlang OTP and therefore runs on top of the Erlang VM. For this reason plugins have to be developed in a programming language that runs on the Erlang VM. The most popular choice is obviously the Erlang programming language itself, but Elixir or Lisp flavoured Erlang LFE could be used too.
Be aware that in VerneMQ a plugin does NOT run in a sandboxed environment and misbehaviour could seriously harm the system (e.g. performance degradation, reduced availability as well as consistency, and message loss). Get in touch with us in case you require a review of your plugin.
This guide explains the different flows that expose different hooks to be used for custom plugins. It also describes the code structure a plugin must comply to in order to be successfully loaded and started by the VerneMQ plugin mechanism.
All the hooks that are currently exposed fall into one of three categories.
Hooks that allow you to change the protocol flow. An example could be to authenticate a client using the auth_on_register
hook.
Hooks that inform you about a certain action, that could be used for example to implement a custom logging or audit plugin.
Hooks that are called given a certain condition
Notice that some hooks come in two variants, for example the auth_on_register
and then auth_on_register_m5
hooks. The _m5
postfix refers to the fact that this hook is only invoked in an MQTT 5.0 session context whereas the other is invoked in a MQTT 3.1/3.1.1 session context.
Before going into the details, let's give a quick intro to the VerneMQ plugin system.
The VerneMQ plugin system allows you to load, unload, start and stop plugins during runtime, and you can even upgrade a plugin during runtime. To make this work it is required that the plugin is an OTP application and strictly follows the rules of implementing the Erlang OTP application behaviour. It is recommended to use the rebar3
toolchain to compile the plugin. VerneMQ comes with built-in support for the directory structure used by rebar3
.
Every plugin has to describe the hooks it is implementing as part of its application environment file. The vmq_acl
plugin for instance comes with the application environment file below:
Lines 6 to 10 instruct the plugin system to ensure that those dependent applications are loaded and started. If you're using third party dependencies make sure that they are available in compiled form and part of the plugin load path. Lines 16 to 20 allow the plugin system to compile the plugin rules. Yes, you've heard correctly. The rules are compiled into Erlang VM code to make sure the lookup and execution of plugin code is as fast as possible. Some hooks exist which are used internally such as the change_config/1
, we'll describe those at some other point.
The environment value for vmq_plugin_hooks
is a list of hooks. A hook is specified by {Module, Function, Arity, Options}
.
To streamline the plugin development we provide a different Erlang behaviour for every hook a plugin implements. Those behaviours are part of the vernemq_dev
library application, which you should add as a dependency to your plugin. vernemq_dev
also comes with a header file that contains all the type definitions used by the hooks.
It is possible to have multiple plugins serving the same hook. Depending on the hook the plugin chain is used differently. The most elaborate chains can be found for the hooks that deal with authentication and authorization flows. We also call them conditional chains as a plugin can give control away to the next plugin in the chain. The image show a sample plugin chain for the auth_on_register
hook.
Most hooks don't require conditions and are mainly used as event handlers. In this case all plugins in a chain are called. An example for such a hook would be the on_register
hook.
A rather specific case is the need to call only one plugin instead of iterating through the whole chain. VerneMQ uses such hooks for it's pluggable message storage system.
Unless you're implementing your custom message storage backend, you probably won't need this style of hook.
The position in the plugin call chain is currently implicitly given by the order the plugins have been started.
The plugin mechanism uses the application environment file to infer the applications that it has to load and start prior to starting the plugin itself. It internally uses the application:ensure_all_started/1
function call to start the plugin. If your setup is more complex you could override this behaviour by implementing a custom start/0
function inside a module that's named after your plugin.
The plugin mechanism uses application:stop/1
to stop and unload the plugin. This won't stop the dependent application started at startup. If you rely on third party applications that aren't started as part of the VerneMQ release, e.g. a database driver, you can implement a custom stop/0
function inside a module that's named after your plugin and properly stop the driver there.
The vmq_types.hrl
exposes all the type specs used by the hooks. The following types are used by the plugin system:
The auth_on_publish
and auth_on_publish_m5
hooks allow your plugin to grant or reject publish requests sent by a client. It also enables to rewrite the publish topic, payload, qos, or retain flag and in the case of auth_on_publish_m5
properties. The auth_on_publish
hook is specified in the Erlang behaviour and the auth_on_publish_m5
hook in the behaviour available in the repo.
The on_publish
and on_publish_m5
hooks allow your plugin to get informed about an authorized publish message. The hook is specified in the Erlang behaviour and the on_publish_m5
hook in the behaviour available in the repo.
The on_offline_message
hook allows your plugin to get notified about a new a queued message for a client that is currently offline. The hook is specified in the Erlang behaviour available in the repo.
The on_deliver
and on_deliver_m5
hooks allow your plugin to get informed about outgoing publish messages, but also allows you to rewrite topic and payload of the outgoing message. The hook is specified in the Erlang behaviour and the on_deliver_m5
hook in the behaviour available in the repo.
The auth_on_register
and auth_on_register_m5
hooks allow your plugin to grant or reject new client connections. Moreover it lets you exert fine grained control over the configuration of the client session. The auth_on_register
hook is specified in the Erlang behaviour and the auth_on_register_m5
hook in the behaviour available in the repo.
The on_auth_m5
hook allows your plugin to implement MQTT enhanced authentication, see .
The on_register
and on_register_m5
hooks allow your plugin to get informed about a newly authenticated client. The hook is specified in the Erlang behaviour and the behaviour available in the repo.
Once a new client was successfully authenticated and the above described hooks have been called, the client attaches to its queue. If it is a returning client using clean_session=false
or if the client had previous sessions in the cluster, this process could take a while. (As offline messages are migrated to a new node, existing sessions are disconnected). The hook is called at the point where a queue has been successfully instantiated, possible offline messages migrated, and potential duplicate sessions have been disconnected. In other words: when the client has reached a completely initialized, normal state for accepting messages. The hook is specified in the Erlang behaviour on_client_wakeup_hook
available in the repo.
This hook is called if an MQTT 3.1/3.1.1 client using clean_session=false
or an MQTT 5.0 client with a non-zero session_expiry_interval
closes the connection or gets disconnected by a duplicate client. The hook is specified in the Erlang behaviour available in the repo.
This hook is called if an MQTT 3.1/3.1.1 client using clean_session=true
or an MQTT 5.0 client with the session_expiry_interval
set to zero closes the connection or gets disconnected by a duplicate client. The hook is specified in the Erlang behaviour available in the repo.
This guide describes how to deploy a VerneMQ cluster on Kubernetes
Kubernetes (K8s) is possibly the most mature technology for deploying Docker containers at scale. While running a single Docker container is supposed to be easy, running a Kubernetes cluster definitely isn't. That's why we recommended to work with a certified Kubernetes partner such as Amazon AWS EKS, Google Cloud GKE, Microsoft Azure AKS, or DigitalOcean.
If your applications already live in Docker containers and are deployed on Kubernetes it can be beneficial to also run VerneMQ on Kubernetes. This guide covers how to successfully deploy a VerneMQ cluster on Kubernetes. Multiple options exist to deploy a VerneMQ cluster at this point. This guide describes how to use the official Helm chart as well as the still experimental Kubernetes Operator.
For the sake of clarity, this guide defines the following terms:
Kubernetes Node: A single virtual or physical machine in a Kubernetes cluster.
Kubernetes Cluster: A group of nodes firewalled from the internet, that are the primary compute resources managed by Kubernetes.
Edge router: A router that enforces the firewall policy for your cluster. This could be a gateway managed by a cloud provider or a physical piece of hardware.
Cluster network: A set of links, logical or physical, that facilitate communication within a cluster according to the Kubernetes networking model.
Service: A Kubernetes Service that identifies a set of pods using label selectors. Unless mentioned otherwise, Services are assumed to have virtual IPs only routable within the cluster network
VerneMQ Cluster: A group of VerneMQ containers that are connected via the Erlang Distribution as well as the VerneMQ clustering mechanism.
This guide assumes that you're familiar with Kubernetes
Helm calls itself the package manager for Kubernetes. In Helm a package is called a chart. VerneMQ comes with such a Helm chart simplifying the initial setup tremendously. If you don't have setup Helm yet, please navigate through their quickstart guide.
Once Helm is properly setup just run the following command in your shell.
This will deploy a single node VerneMQ cluster. Have a look at the possible configuration here.
A Kubernetes Operator is a method of packaging, deploying and managing a Kubernetes application. The VerneMQ Operator is basically just a Pod with the task to deploy a VerneMQ cluster given a so called Custom Resource Definition (CRD). The VerneMQ CRD aims that all required configuration can be made through the CRD and no further configuration should be required. The following command installs the operator along a two node VerneMQ cluster into the namespace messaging
This will result in the following Pods:
And the following cluster status:
At this point you would like to further configure authentication and authorization. The following port forwards may be useful at this point.
kubectl port-forward svc/vernemq-k8s --namespace messaging 1883:1883
kubectl port-forward svc/vernemq-k8s --namespace messaging 8888:8888
In a VerneMQ cluster it doesn't matter to which node a MQTT client connects, subscribes or publishes. A VerneMQ cluster looks like one big MQTT broker to the outside. While this is the main idea of VerneMQ it comes with a cost, namely the data replication/synchronization overhead when 'persistent' clients hop from one pod to the other. As a consequence, we recommend to intelligently choose how to load balance your MQTT clients.
Load balancing in Kubernetes is configured via the Service object. Multiple service types exist:
The ClusterIP type is the default and only permits access from within the Kubernetes cluster. Other pods in the Kubernetes cluster can access VerneMQ via ClusterIP:Port
. The underlying balancing strategy is based on the settings of kube-proxy. Also this type requires that one terminates TLS either in VerneMQ directly or via a different Pod e.g. HAproxy.
The NodePort type uses ClusterIP under the hood but allocates a Port on every Kubernetes node and routes incoming traffic from NodeIP:NodePort
to the ClusterIP:Port
. Like with ClusterIP this type requires that one terminates TLS either in VerneMQ directly or via a different Pod e.g. HAproxy.
The Loadbalancer type uses an external load balancer provided by the cloud provider. In fact this Service type only provides the glue code required to interact with the Loadbalancing services from different cloud providers. If you're running a bare-metal Kubernetes cluster you won't be able to use this Service type, unless you deploy a Kubernetes aware network loadbalancer yourself. Check out MetalLB, which provides a network loadbalancer for bare-metal Kubernetes clusters.
Every Kubernetes node runs a kube-proxy. kube-proxy maps virtual IP addresses to services and creates the required routes in the system so that pods can communicate with each other.
kube-proxy supports multiple modes of operation: - userspace since v1.0 - iptables default since v1.2 - ipvs stable since v1.11, only available if the Kernel of the Kubernetes node supports it.
The performance and scalability characteristics of VerneMQ depend on the proxy-mode and the related configurations. This is especially true for load-balancing specific functionality such as session affinity. E.g. only ipvs supports an efficient way to provide session affinity via the source hashing strategy.
Ingress controllers provide another way to do load balancing and TLS termination in a Kubernetes cluster. However the officially supported ingress controllers nginx and GCE focus on balancing HTTP requests instead of plain TCP connections. Therefore their support for TLS termination is also limited to HTTPS.
Multiple third-party ingress controllers exist, however most of them focus on handling HTTP requests. One of the exceptions is Voyager by AppsCode an ingress controller based on HAProxy, which also efficiently terminates TLS.
Use an external loadbalancer provided by the cloud provider that is capable of terminating TLS and apply a load balancing strategy that provides session affinity e.g. via source hashing.
Terminate TLS outside VerneMQ.
Configure the Pod NodeAffinity correctly to ensure that only one VerneMQ pod is scheduled on any Kubernetes cluster node.
It's preferred to have a smaller number of Pods that are very powerful in terms of available CPU and RAM than the opposite.
How to implement VerneMQ plugins using a HTTP interface
The VerneMQ Webhooks plugin provides an easy and flexible way to build powerful plugins for VerneMQ using web hooks. With VerneMQ Webhooks you are free to select the implementation language to match your technical requirements or the language in which you feel comfortable and productive in. You can use any modern language such as Python, Go, C#/.Net and indeed any language in which you can build something that can handle HTTP requests.
The idea of VerneMQ Webhooks very simple: you can register an HTTP endpoint with a VerneMQ plugin hook and whenever the hook (such as auth_on_register
) is called, the VerneMQ Webhooks plugin dispatches a HTTP post request to the registered endpoint. The HTTP post request contains a HTTP header like vernemq-hook: auth_on_register
and a JSON encoded payload. The endpoint then responds with code 200 on success and with a JSON encoded payload informing the VerneMQ Webhooks plugin which action to take (if any).
To enable webhooks make sure to set:
And then each webhook can be configured like this:
It is possible to have the webhooks plugin omit sending the payload for the auth_on_publish and auth_on_publish_m5 webhooks by setting the no_payload
config:
It is also possible to dynamically register webhooks at run-time:
See which endpoints are registered:
And finally deregistering an endpoint:
We recommend placing the endpoint implementation locally on each VerneMQ node such that each request can go over localhost without being subject to network issues. Also note that currently VerneMQ Webhooks does not encrypt requests in any way or use HTTPS, so care should be taken if the endpoints are made reachable over the network.
Each registered hook uses by default a connection pool containing maximally 100 connections. This can be changed by setting vmq_webhooks.pool_max_connections
to a different value. Similarly the vmq_webhooks.pool_timeout
configuration (value is in milliseconds) can be set to control how long an unused connection should stay in the connection pool before being closed and removed. The default value is 60000 (60 seconds).
These options are available in VerneMQ 1.4.0.
VerneMQ webhooks support caching of the auth_on_register
, auth_on_publish
and auth_on_subscribe
hooks.
This can be used to speed up authentication and authorization tremendously. All data passed to these hooks is used to look if the call is in the cache, except in the case of the auth_on_publish
where the payload is omitted.
To enable caching for an endpoint simply return the cache-control: max-age=AgeInSeconds
in the response headers to one of the mentioned hooks. If the call was successful (authentication granted), the request will be cached together with any modifiers, except for the payload
modifier in the auth_on_publish
hook.
Whenever a non-expired entry is looked up in the cache the endpoint will not be called and the modifiers of the cached entry will be returned, if any.
It is possible to inspect the cache using:
Cache entries are currently not actively disposed after expiry and will remain in memory.
All webhooks are called with method POST
. All hooks need to be answered with the HTTP code 200
to be considered successful. Any hook called that does not return the 200
code will be logged as an error as will any hook with an unparseable payload.
All hooks are called with the header vernemq-hook
which contains the name of the hook in question.
For detailed information about the hooks and when they are called, see the sections Session Lifecycle, Subscribe Flow and Publish Flow.
Note, when overriding a mountpoint or a client-id both have to be returned by the webhook implementation for it to have an effect.
Header: vernemq-hook: auth_on_register
Webhook example payload:
A minimal response indicating the authentication was successful looks like:
It is also possible to override various client specific settings by returning an array of modifiers:
Note, the retry_interval
is in milli-seconds. It is possible to override many more settings, see the Session Lifecycle for more information.
Other possible responses:
Header: vernemq-hook: auth_on_subscribe
Webhook example payload:
A minimal response indicating the subscription authorization was successful looks like:
Another example where where the topics to subscribe have been rewritten looks like:
Note, you can also pass a qos
with value 128
which means it was either not possible or the client was not allowed to subscribe to that specific question.
Other possible responses:
Header: vernemq-hook: auth_on_publish
Note, in the example below the payload is not base64 encoded which is not the default.
Webhook example payload:
A minimal response indicating the publish was authorized looks like:
A more complex example where the publish topic, qos, payload and retain flag is rewritten looks like:
Other possible responses:
Header: vernemq-hook: on_register
Webhook example payload:
The response should be an empty json object {}
.
Header: vernemq-hook: on_publish
Note, in the example below the payload is not base64 encoded which is not the default.
Webhook example payload:
The response should be an empty json object {}
.
Header: vernemq-hook: on_subscribe
Webhook example payload:
The response should be an empty json object {}
.
Header: vernemq-hook: on_unsubscribe
Webhook example payload:
Example response:
Other possible responses:
Header: vernemq-hook: on_deliver
Note, in the example below the payload is not base64 encoded which is not the default.
Webhook example payload:
Example response:
Other possible responses:
Header: vernemq-hook: on_offline_message
Note, in the example below the payload is not base64 encoded which is not the default.
Webhook example payload:
The response should be an empty json object {}
.
Header: vernemq-hook: on_client_wakeup
Webhook example payload:
The response should be an empty json object {}
.
Header: vernemq-hook: on_client_offline
Webhook example payload:
The response should be an empty json object {}
.
Header: vernemq-hook: on_client_gone
Webhook example payload:
The response should be an empty json object {}
.
Header: vernemq-hook: auth_on_register_m5
Webhook example payload:
A minimal response indicating the authentication was successful looks like:
It is also possible to override various client specific settings by returning an array of modifiers:
Note, the retry_interval
is in milli-seconds. It is possible to override many more settings, see the Session Lifecycle for more information.
Other possible responses:
Header vernemq-hook: on_auth_m5
Webhook example payload:
Note, as the authentication data is binary data it is base64 encoded.
A minimal response indicating the authentication was successful looks like:
If authentication were to continue for another round a reason code with value 24 (Continue Authentication) should be returned instead. See also the relevant section in the MQTT 5.0 specification.
Header: vernemq-hook: auth_on_subscribe_m5
Webhook example payload:
A minimal response indicating the subscription authorization was successful looks like:
Another example where where the topics to subscribe have been rewritten looks like:
Note, the forbidden/topic
has been rejected with the qos
value of 135 (Not authorized).
Other responses
Header: vernemq-hook: auth_on_publish_m5
Note, in the example below the payload is not base64 encoded which is not the default.
Webhook example payload:
A minimal response indicating the publish was authorized looks like:
A response where the publish topic has been rewritten:
Other possible responses:
Header: vernemq-hook: on_register_m5
Webhook example payload:
The response should be an empty json object {}
.
Header: vernemq-hook: on_publish_m5
Note, in the example below the payload is base64 encoded .
Webhook example payload:
The response should be an empty json object {}
.
Header: vernemq-hook: on_subscribe_m5
Webhook example payload:
Note, the qos value of 128
(Unspecified error) means the subscription was rejected.
The response should be an empty json object {}
.
Header: vernemq-hook: on_unsubscribe_m5
Webhook example payload:
Example response:
Other possible responses:
Header: vernemq-hook: on_deliver_m5
Note, in the example below the payload is not base64 encoded which is not the default.
Webhook example payload:
Example response:
Other possible responses:
Below is a very simple example of an endpoint implemented in Python. It uses the web
and json
modules and implements handlers for three different hooks: auth_on_register
, auth_on_publish
and auth_on_subscribe
.
The auth_on_register
hook only restricts access only to the user with username joe
and password secret
. The auth_on_subscribe
and auth_on_publish
hooks allow any subscription or publish to continue as is. These last two hooks are needed as the default policy is deny
.
We recommend to use the rebar3
toolchain to generate the basic Erlang OTP application boilerplate and start from there.
Change the rebar.config
file to include the vernemq_dev
dependency:
Compile the application, this will automatically fetch vernemq_dev
.
Now you're ready to implement the hooks. Don't forget to add the proper vmq_plugin_hooks
entries to your src/myplugin.app.src
file.
For a complete example, see the vernemq_demo_plugin.
You need to know about and configure a couple of Operating System and Erlang VM configs to operate VerneMQ efficiently. First, make sure you have set appropriate OS file limits according to our guide here. Second, when you run into performance problems, don't forget to check the settings in the vernemq.conf
file. (Can't open more than 10k connections? Well, is the listener configured to open more than 10k?)
This is the number one topic to look at, if you need to keep an eye on RAM usage.
Context: All network I/O in Erlang uses an internal driver. This driver will allocate and handle an internal application side buffer for every TCP connection. The default size of these buffers will determine your overall RAM use in VerneMQ. The sndbuf and recbuf of the TCP socket will not count towards VerneMQ RAM, but will be used by the Linux Kernel.
VerneMQ calculates the buffer size from the OS level TCP send and receive buffers:
val(buffer) >= max(val(sndbuf),val(recbuf))
Those values correspond to net.ipv4.tcp_wmem
and net.ipv4.tcp_rmem
in your OS's sysctl configuration. One way to minimize RAM usage is therefore to configure those settings (Debian example):
This would result in a 32KB application buffer for every connection.
If your VerneMQ use case requires the use of different TCP buffer optimisations (per groups of clients for instance) you will have to make sure the that the Linux OS buffer configuration, namely net.ipv4.tcp_wmem
and net.ipv4.tcp_rmem
allows for this kind of flexibility, allowing for small TCP buffers and big TCP buffers at the same time.
Example 1 above would allow VerneMQ to allocate minimal TCP read and write buffers of 4KB in the Linux Kernel, a max read buffer of 32KB in the kernel, and a max write buffer of 65KB in the kernel. VerneMQ itself would set its own internal per connection buffer to 65KB in addition.