Some _template options don't work when defined in profile_list profiles

[AlexHill]

https://github.com/jupyterhub/kubespawner/issues/528 touches on this but the issue is more general than described there.

Bug description

Some of the *_template options are expanded in KubeSpawner.__init__() and never again. Overriding them in profile_list profiles therefore doesn't work - you can override the template, but since the template has already been expanded, overriding doesn't produce the desired effect.

See e.g. pvc_name, which is set in init and then used in get_pod_manifest() as-is. Instead, I think pvc_name_template should be expanded in get_pod_manifest().

Expected behaviour

Expansion of templates should be deferred wherever possible so that their overridden values can be respected.

Actual behaviour

Some templates are expanded during init and never again, so overriding them has no effect.

How to reproduce

Deploy z2jh with

  singleuser:
    profileList:
      - display_name: Override test
        default: true
        kubespawner_override:
          service_account: default
          volumes:
            - name: user-home
              persistentVolumeClaim:
                claimName: override-claim-{userid}--{servername}
          volume_mounts:
            - name: user-home
              mountPath: /home/jovyan
          pvc_name_template: override-claim-{userid}--{servername}

And try to launch your server. It will fail, because the volume definitions are expanded after overrides are applied, but the PVC name is not.

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[yuvipanda]

Thanks for opening this, @AlexHill! I agree it makes sense they shouln't be expanded in __init__. Do you think you would be able to make a PR?