In this Bloglet I am going to help you manage your VM host using Xen. Managing Virtual Machines effectively is one of the most important aspects of development and can be approach in a variety of different ways. This is just one of them.
Suppose you have two Xen VM hosts, and that you need to take one of them down for maintenance. Suppose further that there are VMs running on that host that you really don't want to take down. What do you do?
Xen makes it possible to do this: you can hot-migrate a running VM from one Xen host to another. The pre-requisite is that the disk-storage for that VM be stored elsewhere, and accessed by the VM using a remote storage protocol such as NFS.
So, given VM hosts Xen1 and Xen2, and a VM Vm1 running on Xen1, you can go to Xen1 and type:
# xl migrate vm1 Xen2
The result of this is that the VM is suspended, its configuration and the contents of its memory are transferred from Xen1 to Xen2 over the network, and then the new instance on Xen2 is unsuspended.