nova server group policy should be applied when resizing/migrating server

[Chris Friesen]

If I do the following:

nova server-group-create --policy affinity affinitygroup
nova boot --flavor=1 --image=cirros-0.3.1-x86_64-uec --hint group=<group_uuid> cirros0
nova resize cirros0 2

The cirros0 server will be resized but when the scheduler runs it doesn't take into account the scheduling policy of the server group.

I think the same would be true if we migrate the server.

Lastly, when doing migration/evacuation and the user has specified the compute node we might want to validate the choice against the group policy. For emergencies we might want to allow policy violation with a "--force" option or something.

[Dave McCowan (dave-mccowan)]

A similar bug was filed 2012 pointing out that scheduler hints and filters during migration, and a potential patch was submitted.
https://bugs.launchpad.net/nova/+bug/1039065
I'm interested in working on this. Any thoughts on if this should be a bug or a blueprint?

[Chris Friesen (cbf123)]

Curious about why the low priority...it seems to me that anyone that cares enough to use server groups to ensure anti-affinity (or affinity) between servers would want that policy to be taken into account when doing migration/evacuation.

[Charlotte Han (hanrong)]

I also encounter this question.
[root@opencos179-24 ~(keystone_admin)]# nova server-group-list
+--------------------------------------+-------------------+--------------------+------------------------------------------------------------------------------------+----------+
| Id | Name | Policies | Members | Metadata |
+--------------------------------------+-------------------+--------------------+------------------------------------------------------------------------------------+----------+
| 10c20415-5ac0-48ed-aa49-d03fbf57a01f | antiaffinitygroup | [u'anti-affinity'] | [u'66dc1a45-09e7-4b49-ab14-b49e71857c96', u'2adb7114-658d-479a-894b-e2d265387fe2'] | {} |
| ccceb072-dd27-44f2-a98b-14b102c3f883 | affinitygroup | [u'affinity'] | [] | {} |
+--------------------------------------+-------------------+--------------------+------------------------------------------------------------------------------------+---

Instance '66dc1a45-09e7-4b49-ab14-b49e71857c96' and instance '2adb7114-658d-479a-894b-e2d265387fe2' should be on a different host. But after live migration, they are on a same host.

MariaDB [nova]> select uuid,host from instances where deleted=0;
+--------------------------------------+---------------+
| uuid | host |
+--------------------------------------+---------------+
| 2adb7114-658d-479a-894b-e2d265387fe2 | opencos114-93 |
| 66dc1a45-09e7-4b49-ab14-b49e71857c96 | opencos114-93 |
+--------------------------------------+---------------+