Make OVN metadata agent OVNDB read-only

[Jakub Libosvar]

OVN metadata agent runs on each compute node in the cluster and creates an SB DB connection per worker. In large scale deployments this may cause a lot of load on OVN DBs. This bug is to improve OVN metadata agent in a way it won't need connection to the OVN DB leader node but will provide possibility to connect to follower nodes but it will require OVN agent to not perform any writes, because the follower nodes run in read-only mode too.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/neutron/+/792998

[Daniel Alvarez (dalvarezs)]

I think that the words used in the bug description can cause confusion. The leader/follower concept is tied to RAFT (active/active) as per my understanding.

However, the goal of removing the writes for metadata agent I think it's more aligned with the active/backup configuration where clients can't perform writes on the active instance. This way, metadata agents can connect to active and backups indistinctly and put some stress off the active OVSDB server instance where ovn-controller and neutron-server will have to connect to.

[Slawek Kaplonski (slaweq)]

This bug has had a related patch abandoned and has been automatically un-assigned due to inactivity. Please re-assign yourself if you are continuing work or adjust the state as appropriate if it is no longer valid.

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Slawek Kaplonski <email address hidden>" on branch: master
Review: https://review.opendev.org/c/openstack/neutron/+/792998
Reason: This review is > 4 weeks without comment, and failed Zuul jobs the last time it was checked. We are abandoning this for now. Feel free to reactivate the review by pressing the restore button and leaving a 'recheck' comment to get fresh test results.

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Jakub Libosvar <email address hidden>" on branch: master
Review: https://review.opendev.org/c/openstack/neutron/+/792998
Reason: Abandoning this as it requires some scale benchmarking that I don't have hardware for. If it turns out RAFT requires offloading from connections too then we can revive this patch.