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On Wed, Jan 27, 2016 at 5:20 PM, Sean M. Collins <sean at coreitpro.com> wrote:
> On Wed, Jan 27, 2016 at 05:06:03PM EST, Assaf Muller wrote:
>> >> RDO systemd init script for the L3 agent will send a signal 15 when
>> >> 'systemctl restart neutron-l3-agent' is executed. I assume
>> >> Debian/Ubuntu do the same. It is imperative that agent restarts do not
>> >> cause data plane interruption. This has been the case for the L3 agent
>> >
>> > But wouldn't it really be wiser to use SIGHUP to communicate the intent
>> > to restart a process?
>>
>> Maybe. I just checked and on a Liberty based RDO installation, sending
>> SIGHUP to a L3 agent doesn't actually do anything. Specifically it
>> doesn't resync its routers (Which restarting it with signal 15 does).
>
> See, but there must be something that is starting the neutron l3 agent
> again, *after* sending it a SIGTERM (signal 15).

That's why I wrote 'restarting it with signal 15'.

> Then the l3 agent does
> a full resync since it's started back up, based on some state accounting
> done in what appears to be the plugin. Nothing about signal 15 actually
> does any restarting. It just terminates the process.

Yup. The point stands, there's a difference between sig 15 then start,
and a SIGHUP. Currently, Neutron agents don't resync after a SIGHUP
(And I wouldn't expect them to. I'd just expect a SIGHUP to reload
configuration). Restarting an agent shouldn't stop any agent spawned
processes like radvd, keepalived, or perform any clean ups to its
resources (Namespaces, etc), just like you wouldn't want the OVS agent
to destroy bridges and ports, and you wouldn't want a restart to
nova-compute to interfere with its qemu-kvm processes.

>
>> 2016-01-27 20:45:35.075 14651 INFO neutron.agent.l3.agent [-] Agent has just been revived. Doing a full sync.
>
> https://github.com/openstack/neutron/blob/ea8cafdfc0789bd01cf6b26adc6e5b7ee6b141d6/neutron/agent/l3/agent.py#L697
>
> https://github.com/openstack/neutron/blob/ea8cafdfc0789bd01cf6b26adc6e5b7ee6b141d6/neutron/agent/l3/agent.py#L679
>
>
> --
> Sean M. Collins
>
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