[Request] Add support for stream_consumer_max_offset_lag metric from RabbitMQ Prometheus exporter

[pad-master82]

Summary

A new Prometheus metric has been added to RabbitMQ in rabbitmq-server#12765:
stream_consumer_max_offset_lag

This metric is available starting with RabbitMQ 4.0.5, and it represents the maximum offset lag per stream consumer.

Why it matters

In stream-based workloads, tracking consumer lag is critical for:

Identifying slow or stalled consumers

Ensuring real-time processing requirements are met

Troubleshooting throughput bottlenecks

This metric is especially important for teams using RabbitMQ Streams, which is a newer messaging paradigm in RabbitMQ.

Proposal

If possible, it would be great to support this metric in the RabbitMQ OpenMetrics integration.

From looking at the code, maybe it’s as simple as adding the following entry to the _GAUGES list in metrics.py:

_GAUGES = [
    ...
    "rabbitmq_stream_consumer_max_offset_lag": "stream.consumer_max_offset_lag",
]

References

Prometheus metric: stream_consumer_max_offset_lag

Added in: RabbitMQ 4.0.5 (PR #12765)

Related documentation: RabbitMQ Streams