The charm should automatically add new compute to respective AZ

[Andrey Grebennikov]

When utilizing MAAS as the machines supplier, it is possible to retrieve information about the MAAS AZ that the machine belongs to. Juju provides this info as the environment variable JUJU_AVAILABILITY_ZONE.
In case there is the same structure of the availability zones in both MAAS and OpenStack, the charm should automatically add the new compute to the respective OpenStack AZ once deployed.

[Chris MacNaughton (chris.macnaughton)]

This feature already exists in the nova-compute charm. Per the charm readme:

There are two options to provide default_availability_zone config
for nova nodes:

    default-availability-zone
    customize-failure-domain

The order of precedence is as follows:

    1. Information from a Juju provider (JUJU_AVAILABILITY_ZONE)
    if customize-failure-domain is set to True and Juju
    has set the JUJU_AVAILABILITY_ZONE to a non-empty value;

    2. The value of default-availability-zone will be used
    if customize-failure-domain is set to True but no
    JUJU_AVAILABILITY_ZONE is provided via hook
    context by the Juju provider;

    3. Otherwise, the value of default-availability-zone
    charm option will be used.

[Andrey Grebennikov (agrebennikov)]

Chris, I saw this before but it is not working as expected. This is nothing to do with having the machine automatically moved to the AZ.
These two options are only about the config setting in nova.conf of the scheduler, which will dictate the scheduler which AZ to spin up an instance in.

From the nova.conf reference:
"default_availability_zone = nova
This option determines the availability zone to be used when it is not specified in the VM creation request. If this option is not set, the default availability zone ‘nova’ is used."

Moreover, these options of juju do nothing when applied to the computes because the compute isn't responsible for the instance placement.

[James Page (james-page)]

I believe the part that is missing is the automatic creation of host aggregates for OpenStack AZ based on the underlying zone information provided to the charm from Juju.

default_availability_zone should be set on the compute nodes - however the host aggregates also need to be created to ensure that are exposed to end users of the cloud for placement.

[James Page (james-page)]

This should probably be orchestrated by the nova-cloud-controller leader unit - with compute units presenting their zone placement via the relation to nova-cc. Host aggregates can then be created, and I think that the compute hosts will then *just* appear in the right place for placement usage.

[Nobuto Murata (nobuto)]

Those two bugs are possibly duplicates:
https://bugs.launchpad.net/charm-nova-compute/+bug/1873470
https://bugs.launchpad.net/charm-nova-compute/+bug/1888827