[ClusterLabs] Fencing agent fence_xvm using multicast

[Chris Lumens]

>I am trying to get a working fencing device on a single Proxmox 8 host (not using the Proxmox tools) with fence_virtd and fence_virt/vxm. I can't get the command
>    # fence_xvm -o list
>to output anything, it keeps failing via timeout despite many attempts at finding the fault. The exact return message is:
>    Timed out waiting for response
>    Operation failed

If it makes you feel any better, I work on pacemaker and I somewhat
frequently have this problem too.  These are what my notes in my own
personal wiki (vim wiki syntax here) have to say:

= Debugging Fencing =

Fencing with all the VMs and their networking sure is annoying.  The easiest way to make sure
fencing is working is by running the following on both the cluster nodes and the host:

     {{{
     [root at spire audit]# fence_xvm -o list -a 239.255.100.100
     cluster01                        a9e4b6ca-120f-42d5-b5a2-53212d256791 off
     cluster02                        6e0069cd-d7fb-4efc-8473-379095fbdd5f off
     cluster03                        ff3ff2bd-0e3a-4207-9be8-5323cc3f7a87 off
     ctslab-exec                      275f000c-c83f-4b85-a9fb-4b7587836ceb on
     ctslab1                          da19d332-c92b-4d88-8af2-2d8e38fba667 on
     ctslab2                          0eb3f87c-1205-4304-ba33-c0149aac8e3d on
     }}}

If you don't get any output and it takes forever before timing out, here's some things to check:

* Disable firewalld on the host and on the VMs.  It can be made to work, but it's obnoxious and I
   hate it.

* Check `/var/log/audit/audit.log` to make sure there's no selinux problems.  If there are, use
   `audit2allow` to generate policy.  The man pages are helpful here.

* Make sure `/etc/cluster/fence_xvm.key` is the same on the host and all the VMs.  If not, copy it
   over.  Make sure to run `restorecon -Rv /etc/cluster` afterwards.

* Restart `fence_virtd` on the host after installing a new VM or reinstalling an old one.


- Chris