Add support for cross_az_attach option

[Vladimir Grevtsev]

https://docs.openstack.org/nova/queens/configuration/config.html

cross_az_attach
Type: boolean
Default: true
Allow attach between instance and volume in different availability zones.

If False, volumes attached to an instance must be in the same availability zone in Cinder as the instance availability zone in Nova. This also means care should be taken when booting an instance from a volume where source is not "volume" because Nova will attempt to create a volume using the same availability zone as what is assigned to the instance. If that AZ is not in Cinder (or allow_availability_zone_fallback=False in cinder.conf), the volume create request will fail and the instance will fail the build request. By default there is no availability zone restriction on volume attach.

Currently, there is no way to inject this config option to the nova.conf, as this option is under the "cinder" block.

Reason for introducing this: We are planning to start a new deployment for our customer, who was asking for this (e.g they're going to do multi-DC cloud and they would like to have an option to enforce the instances and their volumes being created in a single AZ).

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/710634

[Alex Kavanagh (ajkavanagh)]

Please could you add to the description "why" the option is being added. i.e. what problem is it solving that makes the additional config item to the charm necessary. Thanks.

[Vladimir Grevtsev (vlgrevtsev)]

Hi Alex,

I've updated the description - this config option is being added because of the upcoming deployment for the new customer who was asking for this (e.g they're going to do multi-DC cloud and they would like to have an option to enforce the instances and their volumes being created in a single AZ).

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/710634
Committed: https://git.openstack.org/cgit/openstack/charm-nova-cloud-controller/commit/?id=ab6398463a7fdc0b8ef27c01cbfd2091b1dafca2
Submitter: Zuul
Branch: master

commit ab6398463a7fdc0b8ef27c01cbfd2091b1dafca2
Author: Vladimir Grevtsev <email address hidden>
Date: Sat Feb 29 20:46:23 2020 +0300

    Adding support for cross_az_attach config option.

    Allow attach between instance and volume in different
    availability zones. If False, volumes attached to an
    instance must be in the same availability zone
    in Cinder as the instance availability zone in Nova.

    Change-Id: I21df8e0dfa585133c5ef6a55cdbbc2071c267424
    Closes-Bug: #1856776