[Pacemaker] Resource colocation

[Brice Figureau]

Hi,

With Pacemaker 1.0.4 and Heartbeat 2.99, I need to create a 
configuration which does the following (for example with 2 nodes):
  * apache running on every nodes
  * nginx running on every nodes
  * an IP address running on one node only

This scheme is easy to produce (one clone for apache, one for nginx, a 
standalone resource for the IP).

Now that's where the things get interesting, I want to relocate the IP 
address on another node _if_ nginx fails on the node on which the IP runs.

That's where I'm completely lost. I think I should add a colocation 
rule, but I fail to see which one. I've read the Colocation explained 
documentation and the other documentations, but it's still unclear how 
to model the colocation.

The simplest thing I could think about would be to make a group of IP 
nginx, but in this case nginx doesn't run on every nodes.

Can someone help me?
Thanks!
--
Brice Figureau
My Blog: http://www.masterzen.fr/