Availability-zone types¶

Background¶

In a newly deployed region environment, the volume types (SSD, HDD or others) may only exist on part of the AZs, but end users have no idea which AZ is allowed for one specific volume type and they can’t realize that only when the volume failed to be scheduled to backend. In this case, we have supported availability zone volume type in Rocky cycle which administrators can take advantage of to fix that.

How to config availability zone types?¶

We decided to use type’s extra-specs to store this additional info, administrators can turn it on by updating volume type’s key RESKEY:availability_zones as below:

"RESKEY:availability_zones": "az1,az2,az3"

It’s an array list whose items are separated by comma and stored in string. Once the availability zone type is configured, any UI component or client can filter out invalid volume types based on their choice of availability zone:

Request example:
/v3/{project_id}/types?extra_specs={'RESKEY:availability_zones':'az1'}

Remember, Cinder will always try inexact match for this spec value, for instance, when extra spec RESKEY:availability_zones is configured with value az1,az2, both az1 and az2 are valid inputs for query, also this spec will not be used during performing capability filter, instead it will be only used for choosing suitable availability zones in these two cases below.

1. Create volume, within this feature, now we can specify availability zone via parameter availability_zone, volume source (volume, snapshot, group), configuration option default_availability_zone and storage_availability_zone. When creating new volume, Cinder will try to read the AZ(s) in the priority of:

source group > parameter availability_zone > source snapshot (or volume) > volume type > configuration default_availability_zone > storage_availability_zone

If there is a conflict between any of them, 400 BadRequest will be raised, also now a AZ list instead of single AZ will be delivered to AvailabilityZoneFilter.

2. Retype volume, this flow also has been updated, if new type has configured RESKEY:availability_zones Cinder scheduler will validate this as well.