[Linux-cluster] How to fence a virtual machine in a virtual cluster?

[Gunther Schlegel]

Hi,

I am running RHEL Virtual Machines as cluster services on RedHat 5.2 
Dom0 nodes. The virtual machines use clustered logical volumes for 
storage, /etc/xen is located on a gfs filesystem. Cluster management 
using luci from a dedicated admin server. (The entire system works quite 
well. Some load balancing mechanism on the Dom0 nodes would be fine, but 
that is another issue...)


Now I need a second cluster, in fact I need a gfs filesystem shared 
among some of the virtual machines. In general this should not be an 
issue, but how can I fence a virtual machine inside of a virtual 
cluster? Technically 'virsh destroy' on the Dom0 host will do the job.

Though:
a) I cannot define a script for fencing (at least using luci).
b) There is a fencing method for virtual machines in the RHEL 5.2 
cluster, but it is only meant to fence virtual nodes that are part of a 
mixed cluster of physical and virtual nodes.
c) Inside a virtual cluster the "Virtual Machine Fencing" is of no use, 
because the virtual machine itself is a service in *another* cluster. 
One would need an option to define the Dom0 host or cluster.


I somehow object to mix physical with virtual machines inside of a 
cluster (and I do not want to take virtual machines part in the quorum 
of the physical machines. Hypothetically the virtual machines may fence 
the physical nodes, thereby shutting down the entire cluster...) . The 
Dom0-cluster is intended to run VMs only and no other services. The VMs 
are to provide services, and if they need cluster services, I prefer to 
define aditional clusters.

Am I missing something? In fact the ability to define a script for 
fencing would be sufficient from my point of view.

Or is the only real solution to join the VMs in the Dom0 cluster and 
assign a dedicated failover group to them?

any hint is highly appreciated.

best regards, Gunther





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