[Pacemaker] clusters on virtualised platforms

[Digimer]

On 17/07/14 01:41 PM, Alex Samad - Yieldbroker wrote:
>
>
>> -----Original Message-----
>> From: Digimer [mailto:lists at alteeve.ca]
>> Sent: Thursday, 17 July 2014 2:02 PM
>> To: The Pacemaker cluster resource manager
>> Subject: Re: [Pacemaker] clusters on virtualised platforms
>>
>> Don't confuse quorum and fencing (stonith), they serve different purposes.
>> Basically, quorum is useful when things are working, fencing is required when
>> things go wrong. So regardless of quorum disk, you still need to be able to
>> fence. This requires that each VM be able to call the hypervisor and force a
>> power off.
>
> TA, yep got that, I was thinking and writing ..
>
>>
>> Generally speaking, VM-based cluster nodes are good for learning, but not
>> production. It adds a layer that isn't needed and in HA, simple should trump
>> all else.
>
> Yeah well, it's not really going to change for us, we are virtualised and I can't really see that changing. In fact I would presume you would see more of it.
>
> Thanks

Then ensure that each VM is on a different host, otherwise the host 
itself becomes a single point of failure. Further, you will want to add 
a backup fence method that can take out the host if it stops responding. 
Otherwise, a failure in the host would leave the target node's fence 
method (the hypervisor) inaccessible, and a failed fence method can only 
be handled safely by effectively hanging the cluster. It is not allowed 
that no response be treated as confirmation of node death, lest you end 
up with inevitable split-brains.

I do see people try to do this more often, and I will continue to 
discourage it... "An HA cluster is beautiful not when there is nothing 
left to add, but when there is nothing left to take away.". Every piece 
in the cluster is another potential point of failure.

>>
>> digimer
>>
>> On 17/07/14 12:48 PM, Alex Samad - Yieldbroker wrote:
>>> Hi
>>>
>>> I wonder if there Best practise or how to, on how to run clusters on say
>> VMWare.
>>>
>>> I have built a 2 node cluster with 2 vm's I am hesitant to give rights to each
>> machine to restart the other node. Plus I would have to install the vmware lib
>> and....
>>>
>>> So what do other people do
>>>
>>> Quick search gives me
>>> http://www.hastexo.com/resources/hints-and-kinks/fencing-vmware-
>> virtualized-pacemaker-nodes << But I am not keen on doing that ..
>>>
>>> I am working on centos 6.5
>>>
>>>
>>> Can I use a network resource to make quorum, ie Can the node can ping
>> the dgw ?
>>>
>>> Thanks
>>>
>>>
>>>
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>>>
>>
>>
>> --
>> 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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>> http://oss.clusterlabs.org/mailman/listinfo/pacemaker
>>
>> Project Home: http://www.clusterlabs.org Getting started:
>> http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf
>> Bugs: http://bugs.clusterlabs.org
>
> _______________________________________________
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> http://oss.clusterlabs.org/mailman/listinfo/pacemaker
>
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> Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf
> Bugs: http://bugs.clusterlabs.org
>


-- 
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?