Machine set creation fails if AZ is not selection with OpenStack Provider

[gmaksimov]

What happened

When creating a Machine set (during initial cluster provision or adding to existing cluster), the creation fails if Availability Zone is not selected.
Availability Zone field is not mandatory.

Expected behavior

Option1: Availability Zone field should be mandatory (preferably pre-selected as flavor)
Option2: Availability Zone should be selected by the backend randomly

How to reproduce

Create a Machine set (during initial cluster provision or adding to existing cluster) without specifying Availability Zone (non mandatory field).
The creation fails in the last stage with the following error:
failed to create machine deployment: admission webhook "machine-controller.kubermatic.io-machinedeployments" denied the request: validation failed: failed to get availability zone "": not found

Environment

• UI Version: v2.25.5
• API Version: v2.25.5
• Domain:
• Others: OpenStack provider with 3 AZs.

Current workaround

Select Availability Zone

Affected user persona

Business goal to be improved

Metric to be improved

[gmaksimov]

I would prefer to go with option 1, making the AZ field mandatory and pre-selected with the first AZ by default.
What are your thoughts?

Option1 (Availability Zone field should be mandatory (preferably pre-selected as flavor)

The field can be changed to mandatory here:
https://github.com/kubermatic/dashboard/blob/main/modules/web/src/app/node-data/basic/provider/openstack/component.ts#L167

Error is returned from getAvailabilityZone function of machine-controller:
https://github.com/kubermatic/machine-controller/blob/main/pkg/cloudprovider/provider/openstack/provider.go#L537

Which specifically requires AZ to be selected.
https://github.com/kubermatic/machine-controller/blob/main/pkg/cloudprovider/provider/openstack/helper.go#L109

Option2 (Availability Zone should be selected by the backend randomly)

However, for option2 there is AddDefaults function in machine-controller. It seems to select AZ automatically if there is only 1 AZ. The "random" AZ can be added here.
https://github.com/kubermatic/machine-controller/blob/main/pkg/cloudprovider/provider/openstack/provider.go#L385

[kubermatic-bot]

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