=====Managing mismatches between Nova and libvirt=====


The Nagios sensor 'Nova Libvirt Mismatch' reports the (uuid, instance-id) mappings for VMs that appear in libvirt but not on Nova.

Check the status of this VM in the nova database using the uuid:

<code bash>

$ ssh root@mysql-cluster-01.cloud.pd.infn.it

# mysql
mysql> use nova_prod;
mysql> select display_name,user_id,project_id,created_at,deleted_at from instances where uuid='a2d1589c-f40b-4701-b6d0-687055b8309d';
</code>

If the VM has been deleted according to nova (e.g. the deleted_at field has a value) it is safe to shutdown and then destroy the VM in libvirt. Log on the relevant compute node and issue the following commands (replace instance-000aba38 with the relevant instance-id):


<code bash>

virsh destroy instance-000aba38

virsh undefine instance-000aba38
</code>

If the first command fails with error ''error: Requested operation is not valid: domain is not running'', verify that the VM is already in ''shut off'' state with:

<code bash>
virsh list --all
</code>

and then issue only the ''undefine'' command above.


-----

If the sensor is not installed and it is necessary to find the (uuid, instance-id) mappings for VMs that appear in libvirt but not on Nova:

   * Find the VMs that, according to Nova, are hosted on a specific host (e.g. cld-nl-13.cloud.pd.infn.it):

<code bash>
nova list --all-tenants --host cld-nl-13.cloud.pd.infn.it --fields name,instance_name
</code>

   * Log on that compute node, and see the VMs hosted on that node, according to libvirt:

<code bash>
[root@cld-nl-13 ~]# virsh list
</code>


   * Lets's say that instance ```instance-000aba38``` appears in libvirt but not on Nova.

With the following command:

<code bash>
virsh dumpxml instance-000aba38
</code>

it is possible to see the UUID of this VM (e.g. a2d1589c-f40b-4701-b6d0-687055b8309d).