The check_rabbitmq_cluster NRPE check which checks for cluster partitions is not enabled by default, because it depends on management_plugin=true which is also not enabled by default. I proposed that we resolve this by enabling management_plugin by default.
= Justification/Review of that change =
Partitions are a frequent source of problems in deployments, especially since the default cluster_partition_handling=ignore. They will not self resolve, are not otherwise visible (including in juju status) and in the most frequently used deployment (OpenStack) results in weird and hard to diagnose service failures such as VMs or Networks just not getting connected or fully working, but partly working.
I looked into why this check depends on the management_plugin, which is because the nagios checks run as the 'nrpe' user which does not have access to run 'rabbitmqctl cluster_status'. So the Management API gives a HTTP API to make the request from the unprivileged user to get the same info. Someone did contribute an alternative that runs the cluster_status with cron to output a file that is then read by the nrpe check but it was abandoned and never reviewed (Bug #1548679, https://review.opendev.org/c/openstack/charm-rabbitmq-server/+/538319)
The management API is also useful to have enabled generally, as you can get some good statistics and information from it, to help with support cases including which queues/users are busy, etc, and we have sometimes wanted it in the course of a support case. The API is available to the network over HTTP and currently does not have (at least charmed) SSL support however it does setup authenticated users with a random password, and the user only has 'monitoring' access and there are no users with the administrator tag created by default.
So I think it's safe and sensible to enable by default, but it will result in an extra network service appearing after a charm upgrade, so I guess that should be considered. But I think over-all it would be a positive change especially as the API is otherwise useful and the check is really quite critical.
I'm happy to propose the Merge request to toggle the change, but wanted input if there are any objections to doing so.