Managing server groups

Server groups allow to specify placement policies for the VMs on hypervisors. Two use cases :

• affinity : two VMs workloads are tightly coupled and you wish to keep the VM running on the same hypervisor;

• anti-affinity : N VMs implement a clustered service and you wish to those VMs on seperate hypervisors all the time.

Manage a server group

Create

% openstack server group create --policy anti-affinity mygroup

List

% openstack server group list [--long]
+------------+------------+---------------+-----------------------+------------+---------+
| ID         | Name       | Policies      | Members               | Project Id | User Id |
+------------+------------+---------------+-----------------------+------------+---------+
| 39ca7[...] | mygroup    | anti-affinity | 1c11[...], 93a0c[...] |            |         |
| 56342[...] | un_autre   | affinity      | e747[...]             |            |         |
+------------+------------+---------------+-----------------------+------------+---------+

Display

% openstack server group show mygroup
+----------+-------------------------------------------+
| Field    | Value                                     |
+----------+-------------------------------------------+
| id       | 39ca7dca[...]                             |
| members  | 1c11[...], 93a0c[...]                     |
| name     | mygroup                                   |
| policies | anti-affinity                             |
+----------+-------------------------------------------+

Set a specific group for an instance

First fetch the target group ID with the “server group show” command

% openstack server create --hint group=$GROUPID [...]

Attention

You can fix the server group only at instanciation time, not after.