Rabbitmq nrpe queue check should check for freshness

[Peter Sabaini]

The check_rabbitmq_queue will check a generated stats file, typically created via a cronjob /etc/cron.d/rabbitmq-stats

The check_rabbitmq_queues.py script operates on that generated file but does not check for recentness/freshness of this file. So if for any reason the rabbitmq-stats job gets stuck this check will proceed to happily proclaim rabbit queues OK

To catch this situation check_rabbitmq_queues.py should check if the cached stats file is recent, where "recent" could e.g. mean mtime not older than some multiple of the cronjob period time ago

[Aurelien Lourot (aurelien-lourot)]

https://review.opendev.org/#/c/757955

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/757955
Committed: https://git.openstack.org/cgit/openstack/charm-rabbitmq-server/commit/?id=943f4f63ab256cba61ce9eceb473ed4d671f132e
Submitter: Zuul
Branch: master

commit 943f4f63ab256cba61ce9eceb473ed4d671f132e
Author: Peter Sabaini <email address hidden>
Date: Tue Oct 13 23:14:32 2020 +0200

    Fix: nrpe queue check should check for freshness

    Make the rabbitmq queue check also check if its input data file was
    recently updated. This input data is created via cronjob; if that gets
    stuck we might not actually be getting meaningful data.

    The charm supports configuring the check interval via a full cron time
    specification, so technically one could have that updated only once a
    year even if this doesn't make much sense in a monitoring scenario.

    Also fix a buglet in the nrpe update hook function: only deploy a
    queue check if the cron job hasn't been deconfigured by setting it to
    the empty string

    Change-Id: I60141397f39e3b1b0274230db8d984934c98a08d
    Closes-Bug: #1898523