[ClusterLabs] Moving Related Servers

[Ken Gaillot]

On 04/18/2016 10:05 PM, ‪H Yavari‬ ‪ wrote:
> Hi,
> 
> This is servers maps:
> 
> App 3---------> App 1    (Active)
> 
> App 4 ---------> App 2   (Standby)
> 
> 
> Now App1 and App2 are in a cluster with IP failover.
> 
> I need when IP failover will run and App2 will be Active node, service
> "X" on server App3 will be stop and App 4 will be Active node.
> In the other words, App1 works only with App3 and App 2 works with App 4.
> 
> I have a web application on App1 and some services on App 3 (this is
> same for App2 and App 4)

This is a difficult situation to model. In particular, you could only
have a dependency one way -- so if we could get App 3 to fail over if
App 1 fails, we couldn't model the other direction (App 1 failing over
if App 3 fails). If each is dependent on the other, there's no way to
start one first.

Is there a technical reason App 3 can work only with App 1?

Is it possible for service "X" to stay running on both App 3 and App 4
all the time? If so, this becomes easier.

> 
> Sorry for heavy description.
> 
> 
> ------------------------------------------------------------------------
> *From:* Ken Gaillot <kgaillot at redhat.com>
> *To:* users at clusterlabs.org
> **
> On 04/18/2016 02:34 AM, ‪H Yavari‬ ‪ wrote:
> 
>> Hi,
>>
>> I have 4 CentOS servers (App1,App2.App3 and App4). I created a cluster
>> for App1 and App2 with a IP float and it works well.
>> In our infrastructure App1 works only with App3 and App2 only works with
>> App4. I mean we have 2 server sets (App1 and App3) , (App2 and App4).
>> So I want when server app1 is down and app2 will Online node, App3 will
>> offline too and App4 will Online and vice versa, I mean when App3 is
>> down and App4 will Online, App1 will offline too.
>>
>>
>> How can I do with pacemaker ? we have our self service on servers so how
>> can I user Pacemaker for monitoring these services?
>>
>> Thanks for reply.
>>
>> Regards.
>> H.Yavari
> 
> 
> I'm not sure I understand your requirements.
> 
> There's no way to tell one node to leave the cluster when another node
> is down, and it would be a bad idea if you could: the nodes could never
> start up, because each would wait to see the other before starting; and
> in your cluster, two nodes shutting down would make the cluster lose
> quorum, so the other nodes would refuse to run any resources.
> 
> However, it is usually possible to use constraints to enforce any
> desired behavior. So even those the node might not leave the cluster,
> you could make the cluster not place any resources on that node.
> 
> Can you give more information about your resources and what nodes they
> are allowed to run on? What makes App1 and App3 dependent on each other?