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:

• Docker

Starting VerneMQ

To start a VerneMQ broker, use the vernemq start command in your Shell:

vernemq start

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:

vernemq 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:

q().

Once your broker has started, you can initially check that it is running with the vernemq ping command:

vernemq ping

The command will respond with pong if the broker is running or Node <NodeName> not responding to pings in case it’s not.

Starting using systemd/systemctl

If you use a systemd service file (as in the binary packages), you can start VerneMQ using the systemctl interface to systemd:

$ sudo systemctl start vernemq

Other systemctl commands work as well:

$ sudo systemctl stop vernemq
$ sudo systemctl status vernemq

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:

docker exec vernemq1 vmq-admin cluster show
+--------------------+-------+
|        Node        |Running|
+--------------------+-------+
|VerneMQ@172.17.0.151| true  |
|VerneMQ@172.17.0.152| true  |
+--------------------+-------+

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.

Enabling Session Balancing

To enable session balancing, activate the following two settings in vernemq.conf

 allow_multiple_sessions = on
 queue_deliver_mode = balance

On every VerneMQ node you'll find the vmq-admin command line tool in the release's bin directory (in case you use the binary VerneMQ packages, vmq-admin should already be callable in your path, without changing directories). 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 has different sub-commands with a lot of respective options. You can familiarize yourself by using the --help option on the different levels of vmq-admin. You might see additional sub-commands in case integrated plugins are running (vmq-admin bridge is an example).

$ sudo vmq-admin --help       
Usage: vmq-admin <sub-command>

  Administrate the cluster.

  Sub-commands:
    node        Manage this node
    cluster     Manage this node's cluster membership
    session     Retrieve session information
    retain      Show and filter MQTT retained messages
    plugin      Manage plugin system
    listener    Manage listener interfaces
    metrics     Retrieve System Metrics
    api-key     Manage API keys for the HTTP management interface
    trace       Trace various aspects of VerneMQ
  Use --help after a sub-command for more details.

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.

Status of all listeners

vmq-admin listener show

    +----+-------+------------+-----+----------+---------+
    |type|status |     ip     |port |mountpoint|max_conns|
    +----+-------+------------+-----+----------+---------+
    |vmq |running|192.168.1.50|44053|          |  30000  |
    |mqtt|running|192.168.1.50|1883 |          |  30000  |
    +----+-------+------------+-----+----------+---------+
`

Starting a new listener

vmq-admin listener start address=192.168.1.50 port=1884 --mountpoint /test --nr_of_acceptors=10 --max_connections=1000

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.

Stopping a listener

vmq-admin listener stop address=192.168.1.50 port=1884

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).

Restarting a stopped listener

vmq-admin listener restart address=192.168.1.50 port=1884

Deleting a stopped listener

vmq-admin listener delete address=192.168.1.50 port=1884

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 tell LevelDB how much memory it can use up by setting leveldb.maximum_memory.percent.

Configuring LevelDB memory:

leveldb.maximum_memory.percent = 20

Advanced options

(e)LevelDB exposes a couple of additional configuration values that we link here for the sake of completeness. You can change all the values mentioned in the eleveldb schema file. VerneMQ mostly uses the configured defaults, and for most use cases it should not be necessary to change those.

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:

erlang.distribution.port_range.minimum = 6000
erlang.distribution.port_range.maximum = 7999

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.

listener.vmq.clustering = 0.0.0.0:44053

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.

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:

allow_anonymous
topic_alias_max_broker
receive_max_broker
vmq_acl.acl_file
graphite_host
vmq_acl.acl_reload_interval
graphite_enabled
queue_type