Add an option to disable HAproxy load ballancing

[Tytus Kurek]

At the moment the hacluster charm manages 3 principal services: corosync, pacemaker and haproxy. While the first two are used for HA purposes, the other one is used for LB. As there are currently no existing supported charms for corosync / pacemaker only, it would be good to have an option to disjoint the HA and LB functions.

This requirement comes from a recent experience with a large Swift cluster. It has been observed that Swift Proxy does not cooperate very well with the HAproxy, causing significant performance degradation when creating millions of containers / objects in parallel. Switching HAproxy into single-node mode solves the issue.

Thus, I would like to add an additional option ('enable-load-balancing') to the hacluster charm. This option would be set to 'True' by default, but could be switched to 'False' allowing HAproxy single-node mode. Such an approach would allow us to stay with the unified design across all OpenStack services, while achieving required performance results for the Swift Proxy.

I can elaborate more if needed.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/657786

[Tytus Kurek (tkurek)]

PR for charm-helpers:

https://github.com/juju/charm-helpers/pull/319

[Tytus Kurek (tkurek)]

TBH, I am not happy with the quality of the patches I created, so any feedback from the community would be much appreciated.

[OpenStack Infra (hudson-openstack)]

Change abandoned by Tytus Kurek (<email address hidden>) on branch: master
Review: https://review.opendev.org/657786
Reason: Abandoning as per the discussion.

[Tytus Kurek (tkurek)]

A new PR opened as agreed offline with Alex:

https://github.com/juju/charm-helpers/pull/331

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/662218

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Alex Kavanagh <email address hidden>" on branch: master
Review: https://review.opendev.org/c/openstack/charm-swift-proxy/+/662218
Reason: Abandoning as it's laid vacant for too long; it may be re-opened if the issue still exists.

[Alex Kavanagh (ajkavanagh)]

Currently marking as 'won't fix' as, although some work was done on it, the patch has effectively been abandoned. It may be re-opened if there is still an issue and it needs resolving.