Live migration
Overview
An instance migration is the relocation of an instance from one hypervisor to another.
When an instance has a live migration performed it is not shut down during the process. This is useful when there is an imperative to not interrupt the applications that are running on the instance.
Points to consider:
- network usage may be significantly impacted if block migration mode is used
- instances with intensive memory workloads may require pausing for live migration to succeed
Ensure adequate capacity on the destination host
Oversubscribing the destination host (hypervisor) can lead to service outages. This is only an issue when a destination host is explicitly selected by the operator.
The following commands are useful for discovering a instance’s flavor, listing flavor parameters, and viewing the available capacity of a destination host:
openstack server show <instance-name> -c flavor
openstack flavor show <flavor> -c vcpus -c ram -c disk
openstack hypervisor list
openstack host show <destination-host>
Live migrate an instance
Live migration commands require the user to have the admin role.
To live migrate to any hypervisor with sufficient capacity:
openstack server migrate --live-migration <server-id>
To live migrate to a specific hypervisor:
openstack server migrate --live-migration --os-compute-api-version 2.30 --host <hypervisor-name> <server-id>
If the instance has local storage, you must also specify the --block-migration option:
openstack server migrate --block-migration --live-migration <server id>