cinder backup tries to restore to wrong host

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/cinder/+/816104

Should add the cli steps to be clear.

cinder create --availability-zone az1 1
cinder backup-create <vol-id>
cinder create --backup <backup-id> --availability-zone az1 1

Greetings Sam Morrison,
Are you using RBD for c-vol or iscsi?
Regards,
Sofia

Using RBD

Hello,

The option "backup_use_same_host" partially solves the problem of scheduling restore tasks for backups. As described in the following link, this option allows backup services to use the same backend:
https://docs.openstack.org/cinder/pike/sample_config.html#:~:text=%23backup_use_same_host%20%3D%20false. Therefore, all backup tasks will be scheduled on the same host.

However, this solution has limitations. It only allows restoring backups to the same availability zone (AZ) where the backup was created.
Additionally, managing backups is difficult for users as the "host" field is not visible. Moreover, when creating a volume from a backup or restoring it to a new volume, the AZ must be set explicitly.
Otherwise, the volume will be created in another AZ, to which storage there will be no access from cinder-backup.

As far as I understand, the AZ field is no longer filled for created backups, as seen in this commit:
https://github.com/openstack/cinder/commit/f0211b53b82cde96eb39e9914c3e5fae232db07c

The availability zone is always set to None.

Therefore, when we filtering hosts for task, the AZ not specified, as shown it this part of the code:
https://github.com/openstack/cinder/blob/b75c29c7d8e0e6ac212b59f9ad8d140874e55251/cinder/backup/api.py#L443-L444

This small patch resolved problem with restoring backups.

```
Index: cinder/volume/flows/manager/create_volume.py
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/cinder/volume/flows/manager/create_volume.py b/cinder/volume/flows/manager/create_volume.py
--- a/cinder/volume/flows/manager/create_volume.py (revision f9941d2fb3064d2b9de397fbafe27af5b5247bac)
+++ b/cinder/volume/flows/manager/create_volume.py (date 1679903102534)
@@ -1091,7 +1091,7 @@
             volume.save()

             backup_host = self.backup_api.get_available_backup_service_host(
- backup.host, backup.availability_zone)
+ backup.host, volume.availability_zone)
             updates = {'status': fields.BackupStatus.RESTORING,
                        'restore_volume_id': volume.id,
                        'host': backup_host}
Index: cinder/backup/api.py
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/cinder/backup/api.py b/cinder/backup/api.py
--- a/cinder/backup/api.py (revision f9941d2fb3064d2b9de397fbafe27af5b5247bac)
+++ b/cinder/backup/api.py (date 1679908441677)
@@ -394,7 +394,7 @@
         # Setting the status here rather than setting at start and unrolling
         # for each error condition, it should be a very small window
         backup.host = self._get_available_backup_service_host(
- backup.host, backup.availability_zone)
+ backup.host, volume.availability_zone)
         backup.status = fields.BackupStatus.RESTORING
         backup.restore_volume_id = volume.id
         backup.save()
```

However, it should be noted that this patch does not cover cases where cinder backup service in each availability zone has ...

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/cinder/+/879531

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/cinder/+/879534

Change abandoned by "Denis Nurislamov <email address hidden>" on branch: master
Review: https://review.opendev.org/c/openstack/cinder/+/879531
Reason: invalid

Change abandoned by "Denis Nurislamov <email address hidden>" on branch: master
Review: https://review.opendev.org/c/openstack/cinder/+/879534
Reason: invalid