title: MQTT: Broker messages
agents: mqtt
catalog: app/mqtt
license: GPLv2
distribution: check_mk
description:
 This check monitors message related statistics of a MQTT broker instance.

 It shows the number of currently retained messages active on the broker.
 The number of bytes currently held by message payloads in the message store
 of the broker and the number of currently held messages in the message store.

 Besides these values displaying the current state, it also shows the number
 and size of sent and received messages. It also shows these numbers separately
 for PUBLISH messages and the number of CONNECT messages received.

 To make this check work you have to configure the special agent {agent_mqtt}
 which connects via MQTT to the broker to gather information from the {$SYS/}
 topic.

 This check has been developed with Mosquitto message broker but might also work
 with other brokers. The available values vary from broker to broker and from
 version to version.

 Please note that this check may only be useful if you connect it directly to a
 broker. In case you want to monitor a multi-tentant cluster, this check is
 only useful if configure it for each node since the {$SYS/} topic is is node
 specific. It is not useful to use this check through a load balancer.

 The check is always {OK}.

item:
 The instance ID configured in the special agent.

discovery:
 One service is created for each instance.
