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

[Tim Richards]

Roger,

Thanks for your reply.

As I understand it, for reliable fencing a node cannot be responsible for fencing itself, as it may not be functioning properly. Hence my "cross over" setup. The direct USB connection from Webserver1 to UPS-Webserver2 means that Webserver1 can fence (cut the power to) Webserver2 if the cluster software decides that it is necessary. If my UPSes were able to connect to the network themselves, this would work, but they only have USB or serial inputs for control. 

I am trying to kill two birds with one stone, that is UPS protection from power failure and cluster node fencing (Stonith) with the UPS ability to cut power to a node. Somebody has done this, as there exists a fencing agent using NUT in the Pacemaker/Corosync (Linux-HA cluster software), I just don't know the best way to go about it.

Regards,
Tim.


-----Original Message-----
From: Nut-upsuser [mailto:nut-upsuser-bounces+tims_tank=hotmail.com at lists.alioth.debian.org] On Behalf Of Roger Price
Sent: Friday, 10 February 2017 11:17 PM
To: nut-upsuser Mailing List
Subject: Re: [Nut-upsuser] NUT configuration complicated by Stonith/Fencing cabling

On Sun, 5 Feb 2017, Tim Richards wrote:

> Setup: Active/Passive Two Node Cluster. Two UPSes (APC Smart-UPS 1500 
> C) with USB communication cables cross connected (ie UPS-webserver1 
> monitored by webserver2, and vice versa) to allow for stonith/fencing
> 
> OS OpenSuse Leap 42.2
> NUT version 2.7.1-2.41-x86_64
> Fencing agent: external/nut
> 
> Problem: When power fails to a single UPS, both nodes are shutdown. 
> The node with the still powered UPS comes back up, but requires manual 
> intervention to keep it providing services. I would like only the node 
> with the “On Battery” UPS to shutdown.

I think your title hints at the solution.  What is the advantage of the cross-connection of the UPS units?  Wouldn't it be simpler to have each node connected to the UPS which supplies the power?  This is easier to set up, extends easily to n servers, and is independent of the stonith/fencing which I assume you use for other purposes.

> The resupply of services problem seems to be that NUT on the node that 
> comes back up will not restart until the other node restarts.

With a simpler setup, this problem should go away.

Roger