Migrate instances¶

This section discusses how to migrate running instances from one OpenStack Compute server to another OpenStack Compute server.

Before starting a migration, review the Configure migrations section. Configure live migrations.

Migrating instances

1. Check the ID of the instance to be migrated:

   $ openstack server list
   
   +--------------------------------------+------+--------+-----------------+------------+
   | ID                                   | Name | Status | Networks        | Image Name |
   +--------------------------------------+------+--------+-----------------+------------+
   | d1df1b5a-70c4-4fed-98b7-423362f2c47c | vm1  | ACTIVE | private=a.b.c.d | ...        |
   +--------------------------------------+------+--------+-----------------+------------+
   | d693db9e-a7cf-45ef-a7c9-b3ecb5f22645 | vm2  | ACTIVE | private=e.f.g.h | ...        |
   +--------------------------------------+------+--------+-----------------+------------+
   

2. Check the information associated with the instance. In this example, vm1 is running on HostB:

   $ openstack server show d1df1b5a-70c4-4fed-98b7-423362f2c47c
   
   +----------------------+--------------------------------------+
   | Field                | Value                                |
   +----------------------+--------------------------------------+
   | ...                  | ...                                  |
   | OS-EXT-SRV-ATTR:host | HostB                                |
   | ...                  | ...                                  |
   | addresses            | a.b.c.d                              |
   | flavor               | m1.tiny                              |
   | id                   | d1df1b5a-70c4-4fed-98b7-423362f2c47c |
   | name                 | vm1                                  |
   | status               | ACTIVE                               |
   | ...                  | ...                                  |
   +----------------------+--------------------------------------+
   

3. Select the compute node the instance will be migrated to. In this example, we will migrate the instance to HostC, because nova-compute is running on it:

   $ openstack compute service list
   
   +----+------------------+-------+----------+---------+-------+----------------------------+
   | ID | Binary           | Host  | Zone     | Status  | State | Updated At                 |
   +----+------------------+-------+----------+---------+-------+----------------------------+
   |  3 | nova-conductor   | HostA | internal | enabled | up    | 2017-02-18T09:42:29.000000 |
   |  4 | nova-scheduler   | HostA | internal | enabled | up    | 2017-02-18T09:42:26.000000 |
   |  5 | nova-consoleauth | HostA | internal | enabled | up    | 2017-02-18T09:42:29.000000 |
   |  6 | nova-compute     | HostB | nova     | enabled | up    | 2017-02-18T09:42:29.000000 |
   |  7 | nova-compute     | HostC | nova     | enabled | up    | 2017-02-18T09:42:29.000000 |
   +----+------------------+-------+----------+---------+-------+----------------------------+
   

4. Check that HostC has enough resources for migration:

   # openstack host show HostC
   
   +-------+------------+-----+-----------+---------+
   | Host  | Project    | CPU | Memory MB | Disk GB |
   +-------+------------+-----+-----------+---------+
   | HostC | (total)    |  16 |     32232 |     878 |
   | HostC | (used_now) |  22 |     21284 |     422 |
   | HostC | (used_max) |  22 |     21284 |     422 |
   | HostC | p1         |  22 |     21284 |     422 |
   | HostC | p2         |  22 |     21284 |     422 |
   +-------+------------+-----+-----------+---------+
   

   • cpu: Number of CPUs
   • memory_mb: Total amount of memory, in MB
   • disk_gb: Total amount of space for NOVA-INST-DIR/instances, in GB

   In this table, the first row shows the total amount of resources available on the physical server. The second line shows the currently used resources. The third line shows the maximum used resources. The fourth line and below shows the resources available for each project.

5. Migrate the instance using the openstack server migrate command:

   $ openstack server migrate SERVER --live HOST_NAME
   

   In this example, SERVER can be the ID or name of the instance. Another example:

   $ openstack server migrate d1df1b5a-70c4-4fed-98b7-423362f2c47c --live HostC
   Migration of d1df1b5a-70c4-4fed-98b7-423362f2c47c initiated.
   

   Warning

   When using live migration to move workloads between Icehouse and Juno compute nodes, it may cause data loss because libvirt live migration with shared block storage was buggy (potential loss of data) before version 3.32. This issue can be solved when we upgrade to RPC API version 4.0.

6. Check that the instance has been migrated successfully, using openstack server list. If the instance is still running on HostB, check the log files at src/dest for nova-compute and nova-scheduler to determine why.