[Nut-upsuser] Networked APC

[Charles Lepple]

On 8/1/06, Matthew Isleb <misleb at pnca.edu> wrote:
> On Aug 1, 2006, at 11:05 AM, Charles Lepple wrote:
> > You still may end up with a single point of failure, though, since you
> > probably only want one machine commanding the UPS to power down. (A
> > data center could avoid this with dual-input power supplies fed from
> > separate UPSes.) Someone else who is more familiar with snmp-ups may
> > have more insight into this.
>
> Eh? Why would I want to command the *UPS* to power down? The UPS will
> power down if and when the battery goes dead.
>
> Or did I misunderstand that? I want all my servers to power down
> using the UPS itself as the "master" instead of picking a server as a
> master.

Right, when the UPS sends a low-battery signal (or has been on battery
for X minutes, etc.), you can tell it to shut off the load. This can
be handy if you want to briefly turn something back on during a power
failure.

It's all a matter of taste, of course... but the default NUT
multi-machine setup is to have one "master" that talks to the UPS, and
directs the slaves to shut down. Then, when all the slaves have shut
down, the master shuts down, and sends a power-off signal to the UPS.

Whether the UPS is smart enough to do it, or if NUT has to command the
UPS to power-cycle the load, you probably want a contingency plan for
power-cycling devices if the power returns after machines have already
shut down. This is the most common race condition that inexpensive
UPSes fail to take into account, and it will leave you with a bunch of
halted servers when the power comes back on.

-- 
- Charles Lepple