Rabbitmq: Consider providing a Prometheus variant

[michaelklishin]

This plugin has a variant/tag where it pre-enables the management plugin. Should we add another one that enables RabbitMQ Prometheus plugin instead? Or would it be too much? (we definitely don't want to have a tag per plugin but these two monitoring-related ones are essential)

Enabling both makes sense in some cases and not so much in others. We can assume that Prometheus users would not want to use rabbitmq-management for monitoring.

[gerhard]

I would like to see rabbitmq-prometheus be enabled by default. Because it currently depends on rabbitmq-management, only the management variant can have it enabled by default.

rabbitmq-prometheus overhead is minimal - think /proc subsystem - and metrics are aggregated by default, so no sensitive information will be exposed if this is enabled. A few considerations:

• GET /metrics don't require authentication
• SSL will need to be configured for rabbitmq-prometheus on top of rabbitmq-management
• metrics in rabbitmq-management can be disabled and overhead can be significantly reduced if only rabbitmq-prometheus is used for monitoring

[tianon]

I would like to see rabbitmq-prometheus be enabled by default. Because it currently depends on rabbitmq-management, only the management variant can have it enabled by default.

It only requires rabbitmq_management_agent, right? Not the full management plugin?

rabbitmq-prometheus overhead is minimal - think /proc subsystem - and metrics are aggregated by default, so no sensitive information will be exposed if this is enabled.

I think this sounds pretty reasonable.

Here's what I'd propose:

1. we enable rabbitmq_prometheus in the default variant (which will pull in rabbitmq_management_agent)
2. we include management_agent.disable_metrics_collector = true in the default config
3. in the management variant, we delete the aforementioned default config addition
4. we update docker-entrypoint.sh to handle SSL/TLS for rabbitmq_prometheus just like it does for management and server

My only real concern is the effect this might have on users who aren't using the management variant, but are enabling rabbitmq_management_agent themselves, and if they update their metrics could unexpectedly disappear, and this is what makes me think perhaps a variant for 3.8 makes sense, and we consider enabling by default for the next major release? (Perhaps also coupled with dropping the management variant altogether?)

[gerhard]

It only requires rabbitmq_management_agent, right? Not the full management plugin?

Yes, you are right, I confused it with a past behaviour that has now been addressed 😉

1. we enable rabbitmq_prometheus in the default variant (which will pull in rabbitmq_management_agent)
2. we include management_agent.disable_metrics_collector = true in the default config
3. in the management variant, we delete the aforementioned default config addition
4. we update docker-entrypoint.sh to handle SSL/TLS for rabbitmq_prometheus just like it does for management and server

Yes, this is sensible. Port 15692 (+SSL/TLS) will also need to be exposed.

My only real concern is the effect this might have on users who aren't using the management variant, but are enabling rabbitmq_management_agent themselves, and if they update their metrics could unexpectedly disappear

I can't think of a use-case for enabling rabbitmq_management_agent outside of rabbitmq_management. Can you think of one @michaelklishin?

we consider enabling by default for the next major release?

What major release are you thinking about? If you mean 3.9.x, I don't think that we should wait for this to ship before enabling rabbitmq_prometheus by default.

Perhaps also coupled with dropping the management variant altogether?

I think that this is too useful to drop. Having a UI is valuable to many, especially as many messaging-related operations can be performed from the UI, without requiring a client. I would be more comfortable having Prometheus metrics enabled by default in both rabbitmq & -management variants, rather than introducing a new Prometheus variant.

[tianon]

Ok, that all makes sense! I've started a first pass implementing my proposal in https://github.com/docker-library/rabbitmq/pull/422 which could use some review. :smile: