[ClusterLabs] Need information for N+M clustering using Pacemaker

[Sayed Mujtaba]

Hi ,

Initially My requirement is as below ,

To start with 3+1   (3 active and 1 backup/passive node)

 a) Total 3 number of Active servers 

 b)Each of 3  nodes needs to have different MySQL data bases which needs to
be replicated  (All applications will remain same but data base will get
changed in all 3 active nodes)

c)When out of these 3 nodes  if any node  fails it has to start all
resources on backup/passive node with  the data base of that particular
failed node

Here tricky thing is that all the 3 active servers will be having different
data bases and  when failover happens How it will  start the right data base
in case of failure ? 

I know DRBD will replicate the whole data but I just want to replicate only
data base and start the right data base in case of failover .Any better
solution?


Thanks
-Mujtaba







-----Original Message-----
From: Ken Gaillot [mailto:kgaillot at redhat.com] 
Sent: Thursday, April 16, 2015 6:42 PM
To: users at clusterlabs.org
Subject: Re: [ClusterLabs] Need information for N+M clustering using
Pacemaker

On 04/16/2015 08:52 AM, Sayed Mujtaba wrote:
> I am trying to form M+N clustering along with Load balancer using 
> Pacemaker and not getting the enough information .Can someone please 
> guide me about this set up .
> Cluster from scratch document doesn't cover this topic.

Hi,

It should be as simple as assigning your resources a higher location
preference on your primary nodes than your failover nodes.

However the only reason I can think of to do N+M is if the failover nodes
are less powerful (CPU/RAM/whatever), and that's why you don't want to use
them normally. If your nodes are roughly equivalent, you can just let
Pacemaker spread out the resources on whichever nodes are available. You
don't have to designate particular ones as failover.

Meaning of location constraint scores:

* -INFINITY: never run this resource on this node

* negative: i'd prefer not to run this resource on this node, unless other
factors are more important (for example, no other node is available)

* positive: i'd prefer to run this resource on this node, but it's OK not to
if other factors are more important

* INFINITY: always run this resource on this node if it's available

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