Specifications

Migrating a Domain

Migration is the transferal of a running virtual domain from one physical host to another. Red

Hat Virtualization supports two varieties of migration — offline and live. Offline migration moves

a virtual machine from one host to another by pausing it, transferring its memory, and then

resuming it on the host destination. Live migration does the same thing, but does not directly

affect the domain. When performing a live migration, the domain continues its usual activities,

and from the user perspective is unnoticeable. To initiate a live migration, both hosts must be

running Red Hat Virtualization and the xend daemon. The destinations host must have sufficient

resources (such as memory capacity) to accommodate the domain bandwidth after the

migration. Both the source and destination machines must have the same architecture and

virtualization extensions (such as i386-VT, x86-64-VT, x86-64-SVM, etc.) and must be on the

same L2 subnet.

When a domain migrates its MAC and IP addresses move with it. Only virtual machines with the

same layer-2 network and subnets will successfully migrate. If the destination node is on a

different subnet, the administrator must manually configure a suitable EtherIP or IP tunnel in the

remote node of domain0. The xend daemon stops the domain and copies the job over to the

new node and restarts it. The Red Hat Virtualization RPM does not enable migration from any

other host except the localhost (see the /etc/xend-config.sxp file for information). To allow the

migration target to accept incoming migration requests from remote hosts, you must modify the

target's xen-relocation-hosts-allow parameter. Be sure to carefully restrict which hosts are

allowed to migrate, since there is no authentication.

Since these domains have such large file allocations, this process can be time consuming. If

you migrate a domain with open network connections, they will be preserved on the host

destination, and SSH connections should still function. The default Red Hat Virtualization

iptables rules will not permit incoming migration connections. To allow this, you must create

explicit iptables rules.

You can use the xm migrate command to perform an offline migration :

xm migrate domain-id [destination domain]

You can use the xm migrate command to perform a live migration:

xm migrate domain-id -l [destination domain]

You may need to reconnect to the domain's console on the new machine. You can use the xm

console command to reconnect.

Chapter 11.