[Pacemaker] Migrate/run resource only if m/s resource is master/promoted on target node (follow-up)

[Martin Gombač]

Hi Hj.
First of all thank you for your time.

I'm answering below your suggestions.

hj lee wrote:
> I found a few problems in your configuration.
>
> First why do you set max-master=2? So both nodes are promoted and both 
> nodes are master. Then your colocation constraints does not make 
> sense. Because Hosting has to be started on both nodes. If this is not 
> what you want, then please remove max-master=2. I think the default is 1.
I have to have both drbd devices in primary mode (promoted), so that 
live migration works. Hopefully i can fix my collocation constraints 
with your advice, to make sense for this setup. I wish to tell resource 
manager that Hosting resource can only run, if underlying drbd device is 
in primary mode, if not, then don't bother starting or migrating 
resource there. I wish that Hosting is started only once cluster-wide.
> Second is your location constraint is not quite correct. It does not 
> make sense with colocation.
>
> Location constraint: Please run Hosting in ibm1.
> Colocation: Please run Hosting on drbd master node
>
> The better way to handle this situation will be set location 
> constraint to drbd resource. Using role=master, you can say to 
> Pacemaker which node is preferred node to become drbd master. Once 
> drbd becomes a master in one of nodes, then Hosting will be started on 
> that node based on colocation and order constraint.
We both agree that my config is flaud. :-) What i wanted to say to 
resource manager is, please run Hosting on ibm1, but if you cannot, it 
can be elsewhere where drbd can be or is primary/promoted.
I see where you're going with your suggestions and this would make sense 
for a setup where you could have promoted-demoted/primary-secondary drbd 
setup. However this would break live migration, wich is a requirement.
>
> Please try these two fixes.
I understand your suggestions, but it would break live migration of Xen 
virtual machine called Hosting. Also location constrains get 
auto-magically added when one uses crm interface and issues crm resource 
migrate Hosting ibm1.

Any further suggestions for setup with live migration of HVM would be 
very much appreciated. Setup with live migration of PV machines is easy, 
but doesn't work with HVM. See 
http://blogs.linbit.com/florian/2007/09/03/drbd-806-brings-full-live-migration-for-xen-on-drbd/ 
. Also with that setup one must use dopd and heartbeat to outdate/fence 
resources.

Thank you,
regards,
M.