[Pacemaker] virtual IP or real IP address

[Tim Serong]

 >>> On 10/28/2009 at 07:26 PM, gilberto migliavacca <gbmiglia at yahoo.it> wrote: 
> Hi 
>  
> I have a question. I've seen in the mailing list 
> a lot of example with the IPAddr/IPAddr2 resource agent 
>  
> this resource agent manages the Virtual IP. 
>  
> Could anybody explain me why I have to create a 
> virtual IP istead of using the real IP? 

In brief, the idea is:

- You have (say) two nodes in an HA cluster, each with its
  own unique IP address (i.e. the address you ssh to in order
  to administer that node).
- The "virtual" IP address is a third, different IP, which is
  managed by the IPAddr2 RA.  This is active on only one node
  at a time, and is managed by Pacemaker.
- You set up colocation/ordering constraints so that the
  IPAddr2 resource runs on the same node as an instance of
  Apache (or whatever service you're providing).
- Clients connect to that "virtual" IP, which can then failover to
  the other node, if the node it's running on dies.

HTH,

Tim


-- 
Tim Serong <tserong at novell.com>
Senior Clustering Engineer, Novell Inc.