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vernemq_mqtt_unsubscribe_error.md

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Understand the alert

This alert monitors the number of failed v3/v5 UNSUBSCRIBE operations in VerneMQ in the last minute. If you receive this alert, it means that there is a significant number of failed UNSUBSCRIBE operations, which may impact the MQTT messaging on your system.

What is VerneMQ?

VerneMQ is a high-performance, distributed MQTT message broker. It provides scalable and reliable communication for Internet of Things (IoT) systems and applications.

What is an MQTT UNSUBSCRIBE operation?

An UNSUBSCRIBE operation in MQTT protocol is a request sent by a client to the server to remove one or more topics from the subscription list. It allows clients to stop receiving messages for particular topics.

Troubleshoot the alert

  1. Check VerneMQ logs for any error messages or indications of issues with the UNSUBSCRIBE operation:

    sudo journalctl -u vernemq

Alternatively, you may find the logs in /var/log/vernemq/ directory, if using the default configuration:

   cat /var/log/vernemq/console.log
   cat /var/log/vernemq/error.log

  1. Review the VerneMQ configuration to ensure it is properly set up. The default configuration file is located at /etc/vernemq/vernemq.conf. Make sure that the settings are correct, especially those related to the MQTT protocol version and the supported QoS levels.

  2. Monitor the VerneMQ metrics using the vmq-admin metrics show command. This will provide you with an overview of the broker's performance and help you identify any abnormal metrics that could be related to the failed UNSUBSCRIBE operations:

    sudo vmq-admin metrics show

Pay attention to the mqtt.unsubscribe_error metric, which indicates the number of failed UNSUBSCRIBE operations.

  1. Check the MQTT clients that are sending the UNSUBSCRIBE requests. It is possible that the client itself is misconfigured or has some faulty logic in its communication with the MQTT broker. Review the client's logs and configuration to identify any issues.