Comment 1 for bug 1873470

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.