[Nut-upsuser] NUT configuration complicated by Stonith/Fencing cabling

Tim Richards tims_tank at hotmail.com
Wed Feb 15 23:57:56 UTC 2017


In the interest of completeness, I emailed the author of the NUT fencing agent and asked him about his setup.

His UPSes were all networked, so my USB "cross connected" use, while working, is probably beyond any design specs.

His reply is quoted below.


Hi Tim,

I'm afraid I'm going to disappoint you. We gave up on HA clusters at our site. 
The details of why I gave it up are here:


I can answer some of your questions, though:

- All of our UPSes have network cards.

- That NUT fencing agent script I wrote was not very good at fencing with 
networked APC UPSes. The problem is that there's a couple of seconds delay 
between the UPS changing status and the network interface reporting it 
correctly. It's possible for you to issue the network command to turn power on 
to the UPS, only to have it report "OFF" if you query it again too quickly.

- Because of the networking, every system in the cluster can query every UPS. 
This is important, because if a UPS is supplying power to a switch that connects 
a system (say webserver2) to its UPS (webserver2-ups), then you want to make 
sure that switch is powered by yet another UPS (e.g., switch-ups) so that 
fencing doesn't block communications to the UPS. In the event of a power outage, 
you want the systems to shutdown cleanly if the battery in webserver2-ups OR 
switch-ups is running out.

- To restart a system on my cluster, I issued the network commands to the UPS on 
the STONITHed machine.

- I let the UPS's own "BATTERY LOW" signal tell me when to shut down a system. 
However, I adjusted the parameters to do this at least five minutes before the 
battery ran out. This required annual full calibration of each UPS, to make sure 
I knew that "five minute" estimate was reliable.

- If you want the full gory details, which I think may not be relevant to you, 
you can read my 2013 description of my setup:


Good luck!

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