[ClusterLabs] Fencing with a 3-node (1 for quorum only) cluster

Jan Pokorný jpokorny at redhat.com
Mon Aug 15 08:48:31 EDT 2016

> On 04/08/16 07:21 PM, Dan Swartzendruber wrote:
>> On 2016-08-04 19:03, Digimer wrote:
>>> As for DRAC vs IPMI, no, they are not two things. In fact, I am pretty
>>> certain that fence_drac is a symlink to fence_ipmilan. All DRAC is (same
>>> with iRMC, iLO, RSA, etc) is "IPMI + features". Fundamentally, the fence
>>> action; rebooting the node, works via the basic IPMI standard using the
>>> DRAC's BMC.
>>> [...]
>> At least on CentOS7, fence_ipmilan and fence_drac are not the same.
>> e.g. they are both python scripts that are totally different.
> [...] 
> As for the two agents not being symlinked, OK. It still doesn't change
> the core point through that both fence_ipmilan and fence_drac would be
> acting on the same target.

Just thought I'd add some clarifications:

- in fact fence-agents upstream seems to have thrown the idea of
  proper symlinks away before functionality to that effect was added,
  eventually using file copies instead of symlinks, with the rationale
  "this approach is not recommended so they regular files"

  [Marx&Oyvind, I cannot really imagine what issues this was meant to
  solve nor why it would be not recommended (in Pacemaker, stat calls
  are used that work with symlink targets, not the immediate link
  files, ditto other standard file handling functions), but it seems
  pretty non-systemic compared to, e.g., fence_xvm -> fence_virt:
  and this also makes resulting packages inflated with redundant
  scripts + man pages needlessly;  I'd make a PR for that but it
  seems premature until the recursive make/install issue with
  "symlinked" agents has a definitive conclusion (PR 81+82), but
  basically, you just want 'ln -s SRC DST' instead of 'cp SRC DST']

- fence_ipmilan and fence_drac are indeed not even virtually
  symlinked; quick and dirty way to receive this information, see
  (you may need ' | tr -s " "' just after 'ls -l' command)
  from where you can see that it is fence_idrac which is a virtual
  symlink (same implementation) as fence_ipmilan, while fence_drac
  is an agent on its own

Hope this helps.

Jan (Poki)
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