[Bug 1731595] Re: L3 HA: multiple agents are active at the same time

[Corey Bryant]

SRU details for Ubuntu:

[Impact]
Details of the issue are described thoroughly in this bug report. The fix prevents multiple L3HA masters from existing at the same time, and is already upstream for all affected branches.

[Test Case]
The following SRU process will be followed:
https://wiki.ubuntu.com/OpenStackUpdates

In order to avoid regression of existing consumers, the OpenStack team
will run their continuous integration test against the packages that are
in -proposed.  A successful run of all available tests will be required
before the proposed packages can be let into -updates.

The OpenStack team will be in charge of attaching the output summary of
the executed tests. The OpenStack team members will not mark
‘verification-done’ until this has happened.

[Regression Potential]
The regression potential is lowered as the fix is cherry-picked without change from corresponding upstream stable branches. In order to mitigate the regression potential, the results of the aforementioned tests are attached to this bug.

[Discussion]

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https://bugs.launchpad.net/bugs/1731595

Title:
  L3 HA: multiple agents are active at the same time

Status in Ubuntu Cloud Archive:
  Fix Committed
Status in Ubuntu Cloud Archive ocata series:
  Fix Committed
Status in Ubuntu Cloud Archive pike series:
  Fix Committed
Status in Ubuntu Cloud Archive queens series:
  Fix Committed
Status in neutron:
  Fix Released
Status in neutron package in Ubuntu:
  Fix Released
Status in neutron source package in Zesty:
  Triaged
Status in neutron source package in Artful:
  Fix Committed
Status in neutron source package in Bionic:
  Fix Released

Bug description:
  OS: Xenial, Ocata from Ubuntu Cloud Archive
  We have three neutron-gateway hosts, with L3 HA enabled and a min of 2, max of 3.  There are approx. 400 routers defined.

  At some point (we weren't monitoring exactly) a number of the routers
  changed from being one active, and 1+ others standby, to >1 active.
  This included each of the 'active' namespaces having the same IP
  addresses allocated, and therefore traffic problems reaching
  instances.

  Removing the routers from all but one agent, and re-adding, resolved
  the issue.  Restarting one l3 agent also appeared to resolve the
  issue, but very slowly, to the point where we needed the system alive
  again faster and reverted to removing/re-adding.

  At the same time, a number of routers were listed without any agents
  active at all.  This situation appears to have been resolved by adding
  routers to agents, after several minutes downtime.

  I'm finding it very difficult to find relevant keepalived messages to
  indicate what's going on, but what I do notice is that all the agents
  have equal priority and are configured as 'backup'.

  I am trying to figure out a way to get a reproducer of this, it might
  be that we need to have a large number of routers configured on a
  small number of gateways.

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