Certain publisher metrics are no longer available for MQTT publishers after 3.12.0

[tlperini]

Describe the bug

After upgrading from RabbitMQ 3.11 to 3.12, we noticed that metrics such as rabbitmq_queue_messages_published_total, rabbitmq_channel_messages_delivered_total, rabbitmq_channel_messages_delivered_ack_total and rabbitmq_channel_messages_redelivered_total are no longer available, but only for queues/messages received via the MQTT protocol. Messages received through the AMQP protocol are generating metrics properly.

Our environment:

• RabbitMQ helm chart provided by bitnami (rabbitmq12-0-8)
• Docker image: docker.io/bitnami/rabbitmq:3.12.2-debian-11-r5
• Kubernetes v1.23 (EKS)
• Dedicated persistent PV
• Persistent queues

Reproduction steps

1. Send messages to a specific exchange via the MQTT protocol (considering that this exchange has the proper queue bind).
2. Scrape metrics from the /metrics endpoint
3. Check the rabbitmq_queue_messages_published_total metric for the specific queue
4. The metric doesn't exist ...

Expected behavior

We need the same behavior we had before the upgrade (metrics).

Additional context

No response

[michaelklishin]

This is a known limitations of the MQTT plugin as of 3.12. We don't have an ETA for when certain metrics for MQTT connections might become available again. As plugins decouple of certain internal publishing mechanisms, they become invisible to the current metrics system.

[johanrhodin]

Some more details in this discussion: https://github.com/rabbitmq/rabbitmq-server/discussions/8515