[Linux-cluster] XEN and Cluster Questions

[Nikolas Lam]

On Wed, 2007-10-17 at 11:41 +0200, Marc Grimme wrote:
> Hello,
> we are currently discussing XEN with clustering support. 
> There came some questions we are not sure what the answer is. Perhaps you can 
> help ;-) .
> 
> Background is: We are discussing a group of XEN Dom0 Hosts sharing all devices 
> and files via GFS. They themselves again host a couple of virtually 
> redhat-clustered DomU Hosts with or without gfs.
> 
> 1. Live Migration of cluster DomU nodes:
> When I live migrate a virtual DomU clusternode to another DOM0 XEN Host the 
> migration works ;-) , but the virtual clusternode is thrown out of the 
> cluster. Is this a "works as designed"? I think the problem are the 
> heartbeats not coming in proper time.
> Does that lead to the conclusion that one cannot live migrate cluster nodes?
> 
> 2. Fencing:
> How about fencing of the virtual Dom-U Clusternodes. You are never sure on 
> which Dom-0 Node runs our Dom-U Clusternode. Is the fencing via fence_xvm[d] 
> supported on such an environment? That means how does a virtual DomU 
> clusternode X running on Dom0 Xen Host x know that if virtual DomU 
> clusternode Y running on Dom0 Xen Host y is running there when it is getting 
> the fence request to fence Host y where it is running?
> 
> Thanks Marc.

Hi Marc,

I've not investigated it myself, but if I've understood some Red Hat
Professional Services people correctly, cluster suite has been designed
with this type of application in mind. It's one of the things that
Xen-based virtualisation has over VMWare at the moment.

I think it's the fence_xvm system that informs both the dom0 cluster
nodes and the domU cluster nodes of which dom0 nodes the various domU
nodes are running. (Sorry for that ugly sentence!)

Nik