Welcome to the VerneMQ documentation! This is a reference guide for most of the available features and options of VerneMQ. The might be a good entry point.

For a more general overview on VerneMQ and MQTT, you might want to start with the .

For downloading VerneMQ see .

Installing 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:

• CentOS/RHEL

• Debian/Ubuntu

It is also possible to run VerneMQ using our Docker image:

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.

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.

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:

listener.ws.default = 127.0.0.1:9001

listener.wss.default = 127.0.0.1:9002

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 Eclipse Paho client as well as MQTT.js

You won't be able to open WebSocket connections on a base URL, always add the /mqtt path.

Start a VerneMQ cluster node

docker run --name vernemq1 -d vernemq/vernemq

Sometimes you need to configure a forwarding for ports (on a Mac for example):

docker run -p 1883:1883 --name vernemq1 -d vernemq/vernemq

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.

docker run -e "DOCKER_VERNEMQ_ALLOW_ANONYMOUS=on" --name vernemq1 -d vernemq/vernemq

Autojoining a VerneMQ cluster

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:

docker run -e "DOCKER_VERNEMQ_DISCOVERY_NODE=<IP-OF-VERNEMQ1>" --name vernemq2 -d vernemq/vernemq

(Note, you can find the IP of a docker container using docker inspect <CONTAINER_NAME> | grep \"IPAddress\").

Checking cluster status

To check if the above containers have successfully clustered you can issue the vmq-admin command:

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

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.

For OS Packages

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:

1. 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.

2. Accept the EULA by running sudo vernemq chkconfig or by adding the following line to your vernemq.conf file: accept_eula = yes.

3. 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 , to accept the EULA for the Docker images, the env can be extended with:

env: - name: DOCKER_VERNEMQ_ACCEPT_EULA value: "yes"

Install VerneMQ

Once you have downloaded the binary package, execute the following command to install VerneMQ:

sudo yum install vernemq-<VERSION>.centos7.x86_64.rpm

or:

sudo rpm -Uvh vernemq-<VERSION>.centos7.x86_64.rpm

Activate VerneMQ node

Once you've installed VerneMQ, start it on your node:

service vernemq start

Verify your installation

You can verify that VerneMQ is successfully installed by running:

rpm -qa | grep vernemq

If VerneMQ has been installed successfully vernemq is returned.

Next Steps

Now that you've installed VerneMQ, check out How to configure VerneMQ.

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

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.

Possible Scenario for Message Loss:

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 VerneMQ ensures that convergence regarding subscription data and retained messages is eventually reached.

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:

vmq-admin plugin show

The command above displays all the enabled plugins together with the hooks they implement:

+-----------+-----------+-----------------+-----------------------------+
|  Plugin   |   Type    |     Hook(s)     |            M:F/A            |
+-----------+-----------+-----------------+-----------------------------+
|vmq_passwd |application|auth_on_register |vmq_passwd:auth_on_register/5|
|  vmq_acl  |application| auth_on_publish |  vmq_acl:auth_on_publish/6  |
|           |           |auth_on_subscribe| vmq_acl:auth_on_subscribe/3 |
+-----------+-----------+-----------------+-----------------------------+

Enable a plugin

vmq-admin plugin enable --name=vmq_acl

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.

Disable a plugin

vmq-admin plugin disable --name=vmq_acl

Persisting plugins

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.

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.

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

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.

graphite_enabled = on
graphite_host = carbon.hostedgraphite.com
graphite_port = 2003
graphite_interval = 20000
graphite_api_key = YOUR-GRAPHITE-API-KEY
graphite.interval = 15000

You can further tune the connection to the Graphite server:

# set the connect timeout (defaults to 5000 ms)
graphite_connect_timeout = 10000

# set a reconnect timeout (default to 15000 ms)
graphite_reconnect_timeout = 10000

# set a custom graphite prefix (defaults to '')
graphite_prefix = vernemq

VerneMQ uses Google's LevelDB as a fast storage backend for messages and subscriber information. Each VerneMQ node runs its own embedded LevelDB store.

Configuration of LevelDB memory

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.maximum_memory.percent = 20

Every VerneMQ node has to be configured. Depending on the installation method and chosen platform the configuration file vernemq.conf resides at different locations. If VerneMQ was installed through a Linux package the default location for the configuration file is /etc/vernemq/vernemq.conf.

File Format

• A single setting is handled on one line.

• Lines are structured Key = Value

• Any line starting with # is a comment, and will be ignored

You certainly want to try out VerneMQ right away. For that you could disable authentication like so:

• Set allow_anonymous = on

By default the vmq_acl authorization plugin is enabled and configured to allow publishing and subscribing to any topic, see for more information.

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:

VerneMQ supports enhanced authentication flows or SASL style authentication for MQTT 5.0 sessions. The enhanced authentication mechanism can be used for initial authentication when the client connects or to re-authenticate clients at a later point.

The on_auth_m5 hook allows the plugin to implement SASL style authentication flows by either accepting, rejecting (disconnecting the client) or continue the flow. The on_auth_m5 hook is specified in the Erlang behaviour on_auth_m5_hook in the vernemq_dev repo.

Once you have downloaded the binary package, execute the following command to install VerneMQ:

Note: Replace bionic with appropriate OS version such as focal/trusty/xenial.

You can verify that VerneMQ is successfully installed by running:

If VerneMQ has been installed successfully Status: install ok installed is returned.

Once you've installed VerneMQ, start it on your node:

The whereis vernemq command will give you a couple of directories:

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

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.

Attributions:

In this section the subscription flow is described. VerneMQ provides several hooks to intercept the subscription flow. The most important ones are the auth_on_subscribe and auth_on_subscribe_m5 hooks which act as an application level firewall granting or rejecting subscribe requests.

The auth_on_subscribe and auth_on_subscribe_m5 hooks allow your plugin to grant or reject subscribe requests sent by a client. They also makes it possible to rewrite the subscribe topic and qos. The auth_on_subscribe hook is specified in the Erlang behaviour and the auth_on_subscribe hook in the behaviour available in the repo.

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.

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

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.

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

A great way to monitor VerneMQ is to use Netdata or Netdata Cloud. Netdata uses VerneMQ in its Netdata Cloud service, and has developed full integration with VerneMQ.

This means that you have one of the best monitoring tools ready for VerneMQ. Netdata will show you all the VerneMQ metrics in a realtime dashboard.

When Netdata runs on the same node as VerneMQ it will automatically discover the VerneMQ node.

Learn how to setup Netdata for VerneMQ with the following guide:

https://learn.netdata.cloud/docs/agent/collectors/go.d.plugin/modules/vernemq

The Prometheus exporter is enabled by default and installs an HTTP handler on http://localhost:8888/metrics. To read more about configuring the HTTP listener, see HTTP Listener Configuration.

Example Scrape Config

Add the following configuration to the scrape_configs section inside prometheus.yml of your Prometheus server.

# A scrape configuration containing exactly one endpoint to scrape: 
# Here it's Prometheus itself.
scrape_configs:
  - job_name: 'vernemq'
    scrape_interval: 5s
    scrape_timeout: 5s
    static_configs:
      - targets: ['localhost:8888']

This tells Prometheus to scrape the VerneMQ metrics endpoint every 5 seconds.

Please follow the documentation on the Prometheus website to properly configure the metrics scraping as well as how to access those metrics and configure alarms and graphs.

Authentication

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:

plugins.vmq_passwd = off

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:

allow_anonymous = on

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.

vmq_passwd.password_file = /etc/vernemq/vmq.passwd

The check interval defaults to 10 seconds and can also be defined in the vernemq.conf.

vmq_passwd.password_reload_interval = 10

Setting the password_reload_interval = 0 disables automatic reloading.

Manage Password Files for VerneMQ

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

  Project]() for use in the OpenSSL Toolkit.

• 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.

Topic access is added with lines of the format:

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:

Anonymous users are allowed to

• publish & subscribe to topic bar.

• publish to topic foo.

• subscribe to topic open_to_all.

User john is allowed to

• publish & subscribe to topic foo.

• subscribe to topic baz.

• publish to topic open_to_all.

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.

Queue Deliver mode

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.

queue_deliver_mode = balance

Queue Type

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

We recommend to use the rebar3 toolchain to generate the basic Erlang OTP application boilerplate and start from there.

rebar3 new app name="myplugin" desc="this is my first VerneMQ plugin"
===> Writing myplugin/src/myplugin_app.erl
===> Writing myplugin/src/myplugin_sup.erl
===> Writing myplugin/src/myplugin.app.src
===> Writing myplugin/rebar.config
===> Writing myplugin/.gitignore
===> Writing myplugin/LICENSE
===> Writing myplugin/README.md

Change the rebar.config file to include the vernemq_dev dependency:

{erl_opts, [debug_info]}.
{deps, [{vernemq_dev,
    {git, "git://github.com/vernemq/vernemq_dev.git", {branch, "master"}}}
]}.

Compile the application, this will automatically fetch vernemq_dev.

rebar3 compile                             
===> Verifying dependencies...
===> Fetching vmq_commons ({git,
                                      "git://github.com/vernemq/vernemq_dev.git",
                                      {branch,"master"}})
===> Compiling vernemq_dev
===> Compiling myplugin

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 .

Maximum Client Id Size

Set the maximum size for client ids, MQTT v3.1 specifies a limit of 23 characters.

max_client_id_size = 23

This option default to 23.

Persistent Client Expiration

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.

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.

The VerneMQ HTTP listener is used to serve various VerneMQ subsystems such as:

• Status page

• Prometheus metrics

• management API

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:

To list the retained messages simply invoke vmq-admin retain show:

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.

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

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

A note on statefulness

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:

1. 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.

1. 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):

1. 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.

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:

You can loadtest VerneMQ with our vmq_mzbench tool. It is based on Machinezone's very powerful MZBench system and lets you narrow down what hardware specs are needed to meet your performance goals. You can state your requirements for latency percentiles (and much more) in a formal way, and let vmq_mzbench automatically fail, if it can't meet the requirements.

If you have an AWS account, vmq_mzbench can automagically provision worker nodes for you. You can also run it locally, of course.

1. Install MZBench

Please follow the MZBench installation guide

2. Install vmq_mzbench

Actually, you don't even have to install vmq_mzbench, if you don't want to. Your scenario file will automatically fetch vmq_mzbench for any test you do. vmq_mzbench runs every test independently, so it has a provisioning step for any test, even if you only run it on a local worker.

To install vmq_mzbench on your computer, go through the following steps:

git clone git://github.com/erlio/vmq_mzbench.git
cd vmq_mzbench
./rebar get-deps
./rebar compile

To provision your tests from this local repository, you'll have to tell the scenario scripts to use rsync. Add this to the scenario file:

{make_install, [
{rsync, "/path/to/your/installation/vmq_mzbench/"},
{exclude, "deps"}]},

If you'd just like the script itself fetch vmq_mzbench, then you can direct it to github:

You can familiarize yourself quickly with on writing loadtest scenarios.

There's not much to learn, just make sure you understand how pools and loops work. Then you can add the vmq_mzbench statement functions to the mix and define actual loadtest scenarios.

Currently vmq_mzbench exposes the following statement functions for use in MQTT scenario files:

• random_client_id(State, Meta, I): Create a random client Id of length I

• fixed_client_id(State, Meta, Name, Id): Create a deterministic client Id with schema Name ++ "-" ++ Id

• worker_id(State, Meta): Get the internal, sequential worker Id

It's easy to add more statement functions to the MQTT worker if needed, get in touch with us.

Sometimes you want to have a quick way to test a cluster on your development machine as a VerneMQ developer.

You need to take care of a couple things if you want to run multiple VerneMQ instances on the same machine. There is a make option that let's you build multiple releases, as a commodity, taking care of all the configuration.

First, build a normal release (this is just needed the first time) with:

➜ default git:(master) ✗ make rel

The following command will then prepare 3 correctly configured vernemq.conf files, with different ports for the MQTT listeners etc. It will also build 3 full VerneMQ releases.

➜ default git:(master) ✗ make dev1 dev2 dev3

Check if you have the 3 new releases in the _build directory of your VerneMQ code repo.

You can then start the respective broker instances in 3 terminal windows, by using the respective commands and directory paths. Example:

➜ (_build/dev2/rel/vernemq/bin) ✗ vernemq console

The MQTT listeners will of course be configured differently for each node (the default 1883 port is not used, so that you can still run a default MQTT broker besides your dev nodes). A couple of other ports are also adapted (HTTP status page, cluster communication). The MQTT ports are automically configured in increasing steps of 50: (if in doubt, consult the respective vernemq.conf files)

Note that the dev nodes are not automatically clustered. You still need to manually cluster them with commands like the following:

➜ (_build/dev2/rel/vernemq/bin) ✗ vmq-admin cluster join discovery-node=dev1@127.0.0.1

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.

auth_on_register and auth_on_register_m5

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 auth_on_register_hook and the auth_on_register_m5 hook in the auth_on_register_m5_hook behaviour available in the vernemq_dev repo.

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 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.

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:

Listing the clients and the subscriptions one can do the following:

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.

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 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:

Setting a value for the local node

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.

Setting a value for an arbitrary cluster node

Setting a value for all cluster nodes

Show current VerneMQ config values

For the local node

You can show one or multiple values in a simple table:

For an arbitrary node

For all cluster nodes

Intro

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.

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 .

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 .

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 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:

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 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 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 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 , which provides a network loadbalancer for bare-metal Kubernetes clusters.

Ingress controllers provide another way to do load balancing and TLS termination in a Kubernetes cluster. However the officially supported ingress controllers and 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 by AppsCode an ingress controller based on HAProxy, which also efficiently terminates TLS.

1. 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.

2. Terminate TLS outside VerneMQ.

3. Configure the Pod NodeAffinity correctly to ensure that only one VerneMQ pod is scheduled on any Kubernetes cluster node.

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.

Enabling the bridge functionality

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:

plugins.vmq_bridge = on

See Managing plugins for more information on working with plugins.

When the plugin is enabled a simple status interface is available:

$ vmq-admin bridge show
+-----------------+-----------+----------+-------------------+
|   endpoint      |buffer size|buffer max|buffer dropped msgs|
+-----------------+-----------+----------+-------------------+
|192.168.1.10:1883|     0     |    0     |         0         |
+-----------------+-----------+----------+-------------------+

Sample MQTT Bridge

Setup a bridge to a remote broker:

vmq_bridge.tcp.br0 = 192.168.1.12:1883

Different connection parameters can be set:

# use a clean session (defaults to 'off')
vmq_bridge.tcp.br0.cleansession = off | on

# set the client id (defaults to 'auto', which generates one)
vmq_bridge.tcp.br0.client_id = auto | my_bridge_client_id

# set keepalive interval (defaults to 60 seconds)
vmq_bridge.tcp.br0.keepalive_interval = 60

# set the username and password for the bridge connection
vmq_bridge.tcp.br0.username = my_bridge_user
vmq_bridge.tcp.br0.password = my_bridge_pwd

# set the restart timeout (defaults to 10 seconds)
vmq_bridge.tcp.br0.restart_timeout = 10

# VerneMQ indicates other brokers that the connection
# is established by a bridge instead of a normal client.
# This can be turned off if needed:
vmq_bridge.tcp.br0.try_private = off

# Set the maximum number of outgoing messages the bridge will buffer
# while not connected to the remote broker. Messages published while
# the buffer is full are dropped. A value of 0 means buffering is
# disabled.
vmq_bridge.tcp.br0.max_outgoing_buffered_messages = 100

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 [[[ out | in | both ] qos-level] local-prefix remote-prefix]

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 using in, export messages to a remote broker using out or share messages in both directions. If this parameter is not defined, VerneMQ defaults to out. The QoS level defines the publish/subscribe QoS level used for this topic and defaults to 0. (Source: mosquitto.conf)

The local-prefix and remote-prefix can be used to prefix incoming or outgoing publish messages.

A simple example:

SSL bridges support the same configuration parameters as TCP bridges, but need further instructions for handling the SSL specifics:

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 . 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 CLI tool, and anything that can be done using

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 . Second, when you run into performance problems, don't forget to check the . (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

A typical VerneMQ deployment could from a high level look like the following:

In this scenario MQTT clients connect from the internet and are authenticated and authorized against the Authentication Management Service and publish and receive messages, either with each other or with the Backend-Services which might be responsible for sending control messages to the clients or storing and forwarding messages to other systems or databases for later processing.

To build and deploy a system such as the above a lot of decisions has to be made. These can concern how to do authentication and authorization, where to do TLS termination, how the load balancer should be configured (if one is needed at all), what the MQTT architecture and topic trees should look and how and to what level the system can/should scale. To simplify the following discussion we'll set a few requirements:

• Clients connecting from the internet are using TLS client certificates

VerneMQ can consume a large number of open file handles when thousands of clients are connected as every connection requires at least one file handle.

Most operating systems can change the open-files limit using the ulimit -n command. Example:

However, this only changes the limit for the current shell session. Changing the limit on a system-wide, permanent basis varies more between systems.

On most Linux distributions, the total limit for open files is controlled by sysctl.

As seen above, it is generally set high enough for VerneMQ. If you have other things running on the system, you might want to consult the manpage for how to change that setting. However, what most needs to be changed is the per-user open files limit. This requires editing /etc/security/limits.conf, for which you'll need superuser access. If you installed VerneMQ from a binary package, add lines for the

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).

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.

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.

1. Hooks that allow you to change the protocol flow. An example could be to authenticate a client using the auth_on_register hook.

Introduction and general setup

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:

plugins.vmq_diversity = on

When using database based authentication/authorization the enabled-by-default file based authentication and authorization are most likely not needed and should be disabled:

plugins.vmq_passwd = off
plugins.vmq_acl = off

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.

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:

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:

Sometimes, your Postgresql database requires SSL mode. To connect to it, enable this option :

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:

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:

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:

For MongoDB authentication and authorization configure the following in vernemq.conf:

MongoDB hashing methods:

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:

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.

Developing VerneMQ plugins in Erlang is the most powerful way to extend the functionality of a VerneMQ broker but is a barrier developers not familiar with Erlang. For this reason we've implemented a VerneMQ extension that allows you to develop plugins using the Lua scripting language. This extension is called vmq_diversity and is shipped as part of VerneMQ.

Moreover vmq_diversity provides simple Lua libraries to communicate with MySQL, PostgreSQL, MongoDB, and Redis within your Lua VerneMQ plugins. An additional Json encoding/decoding library as well as a generic HTTP client library provide your Lua scripts a great way to talk to external services.

Configuration

To enable vmq_diversity make sure to set:

plugins.vmq_diversity = on

To specify a script to load when VerneMQ starts can be done like this:

vmq_diversity.myscript1.file = Path/to/Script.lua

It is also possible to dynamically load a Lua script using vmq-admin:

$ vmq-admin script load path=/Abs/Path/To/script.lua

To reload a script after a change:

A VerneMQ plugin typically consists of one or more implemented VerneMQ hooks. We tried to keep the differences between the traditional Erlang based and Lua based plugins as small as possible. Please check out the for more information about the different flows and a description of the different hooks.

Let's start with a first very basic example that implements a basic authentication and authorization scheme.

This subsection describes the data providers currently available to a Lua script. Every data provider is backed by a connection pool that has to be configured by your script.