Merging upstream version 1.44.3.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 49 insertions, 0 deletions

diff --git a/health/guides/vernemq/vernemq_mqtt_pubrel_sent_reason_unsuccessful.md b/health/guides/vernemq/vernemq_mqtt_pubrel_sent_reason_unsuccessful.md
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+### Understand the alert
+
+This alert is related to VerneMQ, a high-performance MQTT broker. It monitors the number of unsuccessful v5 `PUBREL` packets sent in the last minute. If you receive this alert, it means that there was an issue with sending `PUBREL` packets in your VerneMQ instance.
+
+### What does PUBREL mean?
+
+`PUBREL` is a type of MQTT control packet that indicates the release of an application message from the server to the client. It is the third message in the QoS 2 (Quality of Service level 2) protocol exchange, where QoS 2 ensures that a message is delivered exactly once. An unsuccessful v5 `PUBREL` packet means that there was an error during the packet processing, and the message wasn't delivered to the client as expected.
+
+### Troubleshoot the alert
+
+1. Check the VerneMQ logs:
+   
+   VerneMQ logs can give you valuable information about possible errors that might have occurred during the processing of `PUBREL` packets. Look for any error messages or traces related to the `PUBREL` packets in the logs.
+
+   ```
+   sudo journalctl -u vernemq -f
+   ```
+
+   Alternatively, if you're using a custom log location:
+
+   ```
+   tail -f /path/to/custom/log
+   ```
+
+2. Check the MQTT client-side logs:
+
+   Check the logs of the MQTT client that might have caused the unsuccessful `PUBREL` packets. Look for any connection issues, error messages, or traces related to the MQTT protocol exchanges.
+
+3. Ensure proper configuration for VerneMQ:
+   
+   Verify that the VerneMQ configuration settings related to QoS 2 protocol timeouts and retries are correctly set. Check the VerneMQ [documentation](https://docs.vernemq.com/configuration) for guidance on the proper configuration.
+
+   ```
+   cat /etc/vernemq/vernemq.conf
+   ```
+
+4. Monitor VerneMQ metrics:
+
+   Use Netdata to monitor VerneMQ metrics to analyze the MQTT server's performance and resource usage. This can help you identify possible issues with the server.
+
+5. Address network or service issues:
+
+   If the above steps don't resolve the alert, look for possible network or service-related issues that might be causing the unsuccessful `PUBREL` packets. This could require additional investigation based on your specific infrastructure and environment.
+
+### Useful resources
+
+1. [VerneMQ - Official Documentation](https://docs.vernemq.com/)
+2. [MQTT Essentials: Quality of Service 2 (QoS 2)](https://www.hivemq.com/blog/mqtt-essentials-part-6-mqtt-quality-of-service-levels/)
+3. [Netdata - VerneMQ monitoring](https://learn.netdata.cloud/docs/agent/collectors/go.d.plugin/modules/vernemq)
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