On 13/08/14 11:37 AM, Andrey Borzenkov wrote:
В Wed, 13 Aug 2014 08:56:58 -0400
Digimer <li...@alteeve.ca> пишет:
On 13/08/14 08:37 AM, Andrey Borzenkov wrote:
Hi,
Sorry for may be basic question, but it is my first Linux HA project.
I (will) have two node cluster in active/passive configuration -
single application on one node and second as standby; application si
implemented as master/slave clone. Is it possible to prioritize node,
that have active application? So that in case of split brain passive
node gets killed?
Usually this is done using staggered delay for fencing requests. I
think that it may be possible to implement in pacemaker using rules,
but I'm a bit uneasy about how to express it. Rule should select a
node where master is currently active, not fixed node.
Thank you in advance!
-andrei
Hi Andrei,
"Basic questions" is how you avoid mistakes, so please never
apologize for asking them. I sure ask my own basic questions... :P
First up, a little semantics; "split-brain" is what happens when
fencing fails. Your asking what happens when the connection between the
nodes break when both nodes are otherwise happy (sometimes called a
"partitioning of the cluster", though I don't think there is an official
term).
You are right in guessing that it is "delay" to set this. You add the
attribute 'delay="15"' to the fence method. You put the delay attribute
on the node you want to win. Here is an example;
http://clusterlabs.org/wiki/STONITH_Levels#Configuring_The_Fence_Methods
In that example, the node called "pcmk-1" has the 'delay' set, so it
will get a 15 second head start in fencing "pcmk-2". It works that way
because what it does is tell the cluster "If you want to fence 'pcmk-1',
pause for 15 seconds before doing so". So in a 2-node cluster
partitioning, both would initiate a fence against the other immediately,
but pcmk-2 would pause before fencing pcmk-1, where pcmk-1 would *not*
pause before fencing pcmk-2.
It statically assigns priorities to cluster nodes. I need to
dynamically assign higher priority (lower delay) to a node that is
currently running application to ensure that application survives. It
was relatively easy in other cluster products I worked with, but I
cannot figure out how to do it in pacemaker so far.
regards,
-andrei
Hrm, one of the developers would need to speak to this. It may be
possible, but if so, I don't know how.
If I was in that position, I'd probably write a little script that
monitors where the principle service is running and then updates the
config if needed. Something on a 1 minute or 5 minute cron job...
--
Digimer
Papers and Projects: https://alteeve.ca/w/
What if the cure for cancer is trapped in the mind of a person without
access to education?
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