[Pacemaker] resource moving unnecessarily due to ping race condition

[Florian Haas]

>> On 09/08/11 20:59, Brad Johnson wrote:
>>> We have a 2 node cluster with a single resource. The resource must run
>>> on only a single node at one time. Using the pacemaker:ocf:ping RA we
>>> are pinging a WAN gateway and a LAN host on each node so the resource
>>> runs on the node with the greatest connectivity. The problem is when a
>>> ping host goes down (so both nodes lose connectivity to it), the
>>> resource moves to the other node due to timing differences in how fast
>>> they update the score attribute. The dampening value has no effect,
>>> since it delays both nodes by the same amount. These unnecessary
>>> fail-overs aren't acceptable since they are disruptive to the network
>>> for no reason.
>>> Is there a way to dampen the ping update by different amounts on the
>>> active and passive nodes? Or some other way to configure the cluster to
>>> try to keep the resource where it is during these tie score scenarios?

location pingd-constraint group_1 \
  rule $id="pingd-constraint-rule" pingd: defined pingd

May I suggest that you simply change this constraint to

location pingd-constraint group_1 \
  rule $id="pingd-constraint-rule" \
    -inf: not_defined pingd or pingd lte 0

That way, only a host that definitely has _no_ connectivity carries a
-INF score for that resource group. And I believe that is what you
really want, rather than take the actual ping score as a placement
weight (your "best connectivity" approach).

Just my 2 cents, though.

Cheers,
Florian

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