5.3. Preparing to migrate

Before you migrate one or more instances, you need to determine the Compute node names and the IDs of the instances to migrate.

Procedure

Identify the source Compute node host name and the destination Compute node host name:
```
(undercloud)$ source ~/overcloudrc
(overcloud)$ openstack compute service list
```
List the instances on the source Compute node and locate the ID of the instance or instances that you want to migrate:
```
(overcloud)$ openstack server list --host <source> --all-projects
```
Replace <source> with the name or ID of the source Compute node.
Optional: To shut down the source Compute node for maintenance, disable the source Compute node from the undercloud to ensure that the scheduler does not attempt to assign new instances to the source Compute node during maintenance:
```
(overcloud)$ source ~/stackrc
(undercloud)$ openstack compute service set <source> nova-compute --disable
```
Replace <source> with the name or ID of the source Compute node.

If you are not migrating NUMA, CPU-pinned or DPDK instances, you are now ready to perform the migration. Follow the required procedure detailed in Cold migrating an instance or Live migrating an instance.

If you are migrating NUMA, CPU-pinned or DPDK instances, you need to prepare the destination node. Complete the procedure detailed in 「Additional preparation for DPDK instances」.