[RFE] refactor of L3 resources update procedure

[LIU Yulong]

In the L3 meeting 2021-06-30, I mentioned this topic.
https://meetings.opendev.org/meetings/neutron_l3/2021/neutron_l3.2021-06-30-14.00.log.html#l-28

Current L3 resources (floating IPs, router interface, router external gateway) processing procedure is a bit heavy, and sometimes waste of times. For instance, if one floating IP is bind to a port under one router, the steps are:
1. floating IP updated
2. notify L3 agent that this floating IPs router is updated
3. L3 agent sync the router info
4. L3 agent reprocess all router related resources

The alternative is we can use resource cache for router related resources, then the procedure for floating IP update can be changed to:
1. floating IP updated.
2. OVO object update event send out.
3. L3 agents which has the related router resident will do the processing of floating IP only, no sync of full router info, no processing of all router resources again!

This can be a huge performace improvement for L3 related resources processing.

Thoughts?

[Bence Romsics (bence-romsics)]

As usual please bring this topic for discussion to the neutron-drivers meeting:
https://meetings.opendev.org/#Neutron_drivers_Meeting

Please note, due to summer vacations, there's no meeting this week:
http://lists.openstack.org/pipermail/openstack-discuss/2021-July/023518.html

[Slawek Kaplonski (slaweq)]

When I'm thinking more about it, I think that it's not really RFE and we can treat it as an bug/improvement in existing code. So I'm going to remove rfe tag from this LP.