Nut upsuser - Oct 2023 - FSD sequence: Waiting for bigger and slower clients before cutting power

Hi, and thanks for this great piece of free software! I've been meaning to 
sort this out for some time, but we don't get power outages that often, 
fortunately...

So, correct me if I'm wrong, but from the documentation at https://
networkupstools.org/docs/user-manual.chunked/
Configuration_notes.html#UPS_shutdown, and also reading upsmon.c, when a UPS 
goes OB LB (assuming we have a single UPS connected to a primary and supplying 
power to the primary and some number of secondaries), the primary notifies the 
secondaries, the secondaries wait for FINALDELAY and then execute SHUTDOWNCMD 
immediately followed by exiting, thereby disconnecting from the primary, and 
the primary, after seeing all secondaries disconnect, proceed with its 
shutdown (only waiting for FINALDELAY), which ends with telling the UPS to cut 
the power (without delay too, right?).

Again, correct me if I'm wrong, Is it only I who find this a bit flawed? I 
would like for the secondaries to stay connected until they shut down. We have 
a server with a bunch of virtual machines on, and they can take a couple of 
minutes to shut down. Otherwise the primary can easily cut the power 
prematurely. Avoiding this, it seems, could pretty easily be accomplished by 
having upsmon wait, perhaps in a separate loop, for the INT/TERM/QUIT signal 
(it would still be necessary to configure the service manager such that upsmon 
is terminated as late as possible). The primary could start shutting down its 
services in the meantime, but upsmon would hold the poweroff until the 
secondaries have disconnected (or HOSTSYNC expires).

Surely this would be better than cranking up FINALDELAY on the primary and 
always waiting for a fixed period of time, as suggested in
https://alioth-lists.debian.net/pipermail/nut-upsuser/2012-April/007550.html? I
guess I could
try writing a SHUTDOWNCMD script that doesn't exit until most other services
have also done so, taking care not to create a deadlock situation.

Another option would be to use upssched to shut down the "big rig"
earlier. It
just seems unsatisfying to me that upssched is entirely time-based. It would 
be nice if it were easier to trigger off battery.charge or battery.runtime 
going below arbitrary values instead of just the on battery and low battery 
statuses.

How do others solve this?

-- 
Magnus Holmgren
./?\_/?\. Milient
(also holmgren at debian.org)

On Fri, Oct 27, 2023, at 10:25 AM, Magnus Holmgren
wrote:
> Hi, and thanks for this great piece of free software! I've been meaning
to
> sort this out for some time, but we don't get power outages that often,
> fortunately...
>
> So, correct me if I'm wrong, but from the documentation at https://
> networkupstools.org/docs/user-manual.chunked/
> Configuration_notes.html#UPS_shutdown, and also reading upsmon.c, when a
UPS
> goes OB LB (assuming we have a single UPS connected to a primary and
supplying
> power to the primary and some number of secondaries), the primary notifies
the
> secondaries, the secondaries wait for FINALDELAY and then execute
SHUTDOWNCMD
> immediately followed by exiting, thereby disconnecting from the primary,
and
> the primary, after seeing all secondaries disconnect, proceed with its 
> shutdown (only waiting for FINALDELAY), which ends with telling the UPS to
cut
> the power (without delay too, right?).
>
> Again, correct me if I'm wrong, Is it only I who find this a bit
flawed? I
> would like for the secondaries to stay connected until they shut down. We
have
> a server with a bunch of virtual machines on, and they can take a couple of
> minutes to shut down. Otherwise the primary can easily cut the power 
> prematurely. Avoiding this, it seems, could pretty easily be accomplished
by
> having upsmon wait, perhaps in a separate loop, for the INT/TERM/QUIT
signal
> (it would still be necessary to configure the service manager such that
upsmon
> is terminated as late as possible). The primary could start shutting down
its
> services in the meantime, but upsmon would hold the poweroff until the 
> secondaries have disconnected (or HOSTSYNC expires).
I'm not talking directly to your point, however it is a related area.

What I want to do, and have not yet:

* shutdown the primary servers first (i.e. the two Dell R730 in the basement)
* leave the gateway device (small box, very little power and the switches
running)
* when battery gets down a bit farther, shutdown the rest of the gear

Power outages aren't common for me, so I might be able to keep my home
internet running for another 40 minutes or so, which might be a good thing.

-- 
  Dan Langille
  dan at langille.org

Hi, this does sound like a useful idea - although for the principle of
least surprise and for variation in deployments, I'd rather have it as a
(non-default state of a) configuration toggle that can be set via
`upsmon.conf`: whether this particular client exits after processing FSD or
not. The onus for the rest would be on general systems integration - e.g.
ensure that init scripts `K*`ill the long-running services before they go
after upsmon and upsd, or add a drop-in systemd config snippet for
nut-monitor to not-conflict with "shutdown.target" (and half a dozen
of its
equivalents for halt/reboot/poweroff/...), and possibly to break the
shutdown-dependency between nut-monitor/nut-server/nut-driver units.

On a related note - there was lately work to allow daemonized drivers to
kill power of the UPS (may be useful especially for devices with long
protocol init times), with a safety switch to flip about this and actually
allow the driver to issue killpower commands. So stopping driver daemons
might eventually be not needed - but I'm not sure any OS integrations took
note of this possibility yet. It was not officially released so far, just
is in master branch.

Note however that typically FSD happens when the power is critical.
Definitions of that vary, as well as ability or not to set certain
thresholds for when the device would emit (and a driver would relay) the
low-battery condition. You might not physically have those 2 minutes worth
of remaining battery charge to shut down the VMs or other long-stopping
services (e.g. app servers to flush in-flight operations, and only later
their databases) - more so with the probable storage I/O and power-draw
burst to flush out databases or hibernate those VMs.

In this case fiddling with upssched or setting up dummy-ups relays with an
override for defining earlier trigger of critical state (usually by battery
charge or time remaining) may fare better: your NUT primary server would
seem to serve several UPSes (the "real" device and a few dummies with
different "criticality" levels), and various secondary hosts would
MONITOR
the suitable dummy to begin their shutdown earlier into the outage. This
approach may also be useful for Dan's post :)

Jim

On Fri, Oct 27, 2023 at 4:55?PM Magnus Holmgren <
magnus.holmgren at milientsoftware.com> wrote:
> Hi, and thanks for this great piece of free software! I've been meaning
to
> sort this out for some time, but we don't get power outages that often,
> fortunately...
>
> So, correct me if I'm wrong, but from the documentation at https://
> networkupstools.org/docs/user-manual.chunked/
> Configuration_notes.html#UPS_shutdown, and also reading upsmon.c, when a
> UPS
> goes OB LB (assuming we have a single UPS connected to a primary and
> supplying
> power to the primary and some number of secondaries), the primary notifies
> the
> secondaries, the secondaries wait for FINALDELAY and then execute
> SHUTDOWNCMD
> immediately followed by exiting, thereby disconnecting from the primary,
> and
> the primary, after seeing all secondaries disconnect, proceed with its
> shutdown (only waiting for FINALDELAY), which ends with telling the UPS to
> cut
> the power (without delay too, right?).
>
> Again, correct me if I'm wrong, Is it only I who find this a bit
flawed? I
> would like for the secondaries to stay connected until they shut down. We
> have
> a server with a bunch of virtual machines on, and they can take a couple
> of
> minutes to shut down. Otherwise the primary can easily cut the power
> prematurely. Avoiding this, it seems, could pretty easily be accomplished
> by
> having upsmon wait, perhaps in a separate loop, for the INT/TERM/QUIT
> signal
> (it would still be necessary to configure the service manager such that
> upsmon
> is terminated as late as possible). The primary could start shutting down
> its
> services in the meantime, but upsmon would hold the poweroff until the
> secondaries have disconnected (or HOSTSYNC expires).
>
> Surely this would be better than cranking up FINALDELAY on the primary and
> always waiting for a fixed period of time, as suggested in
>
https://alioth-lists.debian.net/pipermail/nut-upsuser/2012-April/007550.html?
> I guess I could
> try writing a SHUTDOWNCMD script that doesn't exit until most other
> services
> have also done so, taking care not to create a deadlock situation.
>
> Another option would be to use upssched to shut down the "big
rig"
> earlier. It
> just seems unsatisfying to me that upssched is entirely time-based. It
> would
> be nice if it were easier to trigger off battery.charge or battery.runtime
> going below arbitrary values instead of just the on battery and low
> battery
> statuses.
>
> How do others solve this?
>
> --
> Magnus Holmgren
> ./?\_/?\. Milient
> (also holmgren at debian.org)
>
>
>
> _______________________________________________
> Nut-upsuser mailing list
> Nut-upsuser at alioth-lists.debian.net
> https://alioth-lists.debian.net/cgi-bin/mailman/listinfo/nut-upsuser
>
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