KVM : Live Migration2020/08/05

This is the example to use Live Migration feature for Virtual Machines.

It requires 2 KVM host server and a storage server like follows.
Configure DNS or hosts to resolve names or IP addresses normally, first.

                      +----------------------+
                      |   [  NFS Servver  ]  |
                      |     nfs.srv.world    |
                      |                      |
                      +-----------+----------+
                                  |10.0.0.35
                                  |
+----------------------+          |          +----------------------+
|  [   KVM Host #1  ]  |10.0.0.21 | 10.0.0.22|  [  KVM Host #2   ]  |
|                      +----------+----------+                      |
|   kvm01.srv.world    |                     |    kvm02.srv.world   |
+----------------------+                     +----------------------+

[1]	Configure Storage server that virtual machine images are placed. For Storage server, it's OK to use NFS, iSCSI, GlusterFS and so on. On this example, configure with NFS backend.
[2]	Configure 2 KVM host server and mount a directory provided from Storage server on the same mount point on both KVM server. It uses [/var/kvm/images] for mount point on this example.
[3]	Create and Start a Virtual Machine on a KVM Host and run Live Migration like follows. Before Migration, it needs to set SSH key-pair or other settings to use SSH connection with root user account.

# edit setting of a VM

root@kvm01:~#

virsh edit ubuntu2004

 <disk type='file' device='disk'>
      # add: change cache mode to [none]
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/var/kvm/images/ubuntu2004.img'/>

root@kvm01:~#

virsh start ubuntu2004

root@kvm01:~#

virsh list

 Id    Name                           State
----------------------------------------------------
 1     ubuntu2004                     running

root@kvm01:~#

virsh migrate --live ubuntu2004 qemu+ssh://10.0.0.22/system

root@kvm01:~#

virsh list

 Id    Name             State
--------------------------------------

# just migrated

### on another KVM Host ###

root@kvm02:~#

virsh list

 Id    Name                           State
----------------------------------------------------
 1     ubuntu2004                     running

# back to the KVM Host again like follows

root@kvm02:~#

virsh migrate --live ubuntu2004 qemu+ssh://10.0.0.21/system

root@kvm02:~#

virsh list

 Id    Name             State
--------------------------------------

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