[Pacemaker] Dependency Trees

[Donald Stahl]

> shouldn't be too hard
Whenever you make something idiot proof, the universe invents a bigger idiot.

I'm that idiot I guess.

> use colocation constraints for the things that need to run on the same node
Except colocation resources also include order unless you specifically
tell it that the items are not sequential (At least in my testing).

Furthermore- you can't have a colocation resource of colocation
resources. Nor can you have a group of colocation resources.

You also can't have a group of groups.

I'd love to be able to create a group called "filesystem" that
includes all of the file system mounts I have- and then be able to
create a group that includes the listener, the IP, and the filesystem
group- except you can't have a group of groups. And if I try to create
a group with the listener, the IP and the individual filesystems- then
I can't create another group that also includes those filesystems
because they're already in a group.

I realize this "shouldn't be too hard" but I honestly can't come up
with a way to replicate the VCS behavior with pacemaker. I can create
something that roughly approximates it- but it isn't the same.

It's possible pacemaker can't articulate these ideas- and if so-
that's fine. I'll work around it. I think the more likely explanation
is that I don't fully understand the limitations and use of
colocations, orders and groups. If someone can point me at a thorough
explanation of when you would choose a group over a colocation with an
order and/or the specific limitations of each- I would be grateful.

-Don