KVM : Live Migration2025/01/17

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

It requires 2 KVM host server and also 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  ]  |10.0.0.30 | 10.0.0.51|  [  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. It uses NFS on this example.
[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]	On KVM Hosts, if SELinux is enabled and also uses NFS shared directory, change rules like follows.

[root@kvm01 ~]#

setsebool -P virt_use_nfs on

[4]	On KVM Hosts, if Firewalld is running, allow ports.

[root@kvm01 ~]#

firewall-cmd --add-service={libvirt,libvirt-tls}

[root@kvm01 ~]#

firewall-cmd --add-port=49152-49215/tcp

[root@kvm01 ~]#

firewall-cmd --runtime-to-permanent

[5]	Create and Start a Virtual Machine on a KVM Host and run Live Migration like follows. For connection between KVM Hosts, they connects to others with SSH, so it had better to set SSH key-pair with root account before running live migration.

# edit the setting of a VM you'd like to run live migration

[root@kvm01 ~]#

virsh edit centos10

 <disk type='file' device='disk'>
      # add : change cache mode to [none]
      <driver name='qemu' type='qcow2' cache='none' discard='unmap'/>
      <source file='/var/kvm/images/centos10.img'/>

[root@kvm01 ~]#

virsh start centos10

[root@kvm01 ~]#

virsh list

 Id   Name       State
--------------------------
 2    centos10   running

[root@kvm01 ~]#

virsh migrate --live centos10 qemu+ssh://kvm02.srv.world/system

[root@kvm01 ~]#

virsh list

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

# running virtual machines have been moved

### on another KVM Host ###

[root@kvm02 ~]#

virsh list

 Id   Name       State
--------------------------
 1    centos10   running

# back to the KVM Host again like follows

[root@kvm02 ~]#

virsh migrate --live centos10 qemu+ssh://kvm01.srv.world/system

[root@kvm02 ~]#

virsh list

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

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