Hello Alexander,
you're right, catching up with all the running session and restoring the
full internal state would be a nightmare. I think it is doable but too
difficult (and labour-costly) to get it right. Regarding the need for
graceful restart support anyway, I don't see much of a good reason to
prefer this over a regular graceful restart.
Maria
On 6/21/23 13:41, Alexander Zubkov wrote:
Hello Maria,
Regarding restarts, I think the killer feature might be some sort of
restart, when bird execs a new binary, keeping all the file
descriptors open and its state somehow. So the new instance could
transparently catch up with all the running sessions, etc. It can
serialize the internal state somehow and then reinitialize it from
that. But I'm afraid it would require a great effort to implement
something like that.
On Wed, Jun 21, 2023, 08:58 Maria Matejka via Bird-users
wrote:
Hello Daniel,
On 21 June 2023 01:03:50 CEST, "Daniel Gröber"
wrote:
>Hi Erin,
>
>On Tue, Jun 20, 2023 at 08:20:50PM +0200, Erin Shepherd wrote:
>> I run bird on a system which uses systemd as a service
supervisor, and
>> would like to implement graceful restart in a way which works
well with
>> it.
>
>I'm also interested in getting this working. I'm wondering how
graceful
>restart is supposed to behave to begin with though. Last time I
just tried
>`birdc graceful restart` I was surprised that this actually makes
bird exit
>with rv=0 instead of ... well actually restarting.
>
>Is that normal or a bug in the Debian packaging/systemd service?
You're supposed to start BIRD again on your terms. It's a
misleading command wording, kind of. I don't know whether it's a
good idea to actually exec from the shutdown cycle. Will think
about it. It may be a nice feature.
>I suppose if you're supposed to use graceful restart just before
rebooting
>the system it makes sense but at the time I just wanted to do a full
>restart to update the running bird executable without causing traffic
>disruption and was rather surprised when it didn't come back up.
Yes, these two different use cases were what we were choosing from
when implementing this.
>> In particular, what I'd like to do is:
>> • If I restart the bird service (e.g. for an upgrade), Bird
performs a graceful restart
>> • If I manually stop bird (systemctl stop bird2), shutdown the
system, or any other action which is liable to cause a longer
period of downtime, perform a graceful restart (for BGP at least)
>
>When you want to tickle special behaviour out of systemd I found
it best to
>not try and do everything in one unit. Using the dependency
system you can
>stop another unit before bird.service gets stopped, this can then
call
>birdc graceful restart, like this:
>
>bird-graceful-restart.service:
>
> [Unit]
> After=bird.service
> Requires=bird.service
> [Service]
> Type=oneshot
> RemainAfterExit=yes
> ExecStop=birdc graceful restart
> [Install]
> WantedBy=bird.service
>
>That way you can enable/disable system wide graceful bird restart by
>`systemctl enable bird-graceful-restart.service`.
>
>The BindsTo+After means stopping bird.service (which is part of
restart)
>will first stop bird-graceful-restart.service, which can then
casually
>signal bird to perform graceful restart without a race (I
>think). WanteBy=bird.service is needed as ExecStop will only run
when a
>service has actually been started.
>
>Also some special handling for the case where bird is already
gone (crashed
>or exited) and birdc would fail might be needed. Excercise for
the reader :)
>
>Doing some quick testing this actually seems to do what I want.
Somewhat
>unexpectedly `systemctl restart bird.servce` with the above
enabled does
>then actually do what you'd expect since restart is just
stop+start. Bird
>will exit on getting the graceful restart command so systemd
can't try to
>stop it some more but the subsequent start will make it come back
up. Neat.
>
>On system shutdown only the stop part will happen so bird exiting is
>actully useful now and that too should work as expected.
If there was somebody to implement this additional Systemd unit
and provide it as a patch, we'd happily merge it.
Thank you for all the ideas!
Maria
--
Maria Matejka (she/her) | BIRD Team Leader | CZ.NIC, z.s.p.o.
--
Maria Matejka (she/her) | BIRD Team Leader | CZ.NIC, z.s.p.o.
