simplify singleuser server image parsing by removing stanza from hubploy.yaml and use the default z2jh method

[shaneknapp]

resolves #126

now, you can specify an image in either/both staging.yaml and prod.yaml to specify an image to run in that environment (staging or prod). this will override any image spec defined in common.yaml.

example:

jupyterhub:
  singleuser:
    image:
      name: us-central1-docker.pkg.dev/cal-icor-hubs/user-images/testing-user-image
      tag: da1afdf45dfa

here's the order of presidence for how the image/tag will be set:

• if the image spec is defined in prod or staging.yaml, that will be used.
• if neither of those are specified, then it will default to what's in common.yaml

doing it this way allows us to remove nearly all of the convoluted logic around specifying the image! our CI/CD will need to be updated to use the new image hash, but that's pretty straightforward.

this is still a WIP, as there are some config parsing weirdnesses that i need to think about. specifically, if there is both no images: stanza in hubploy.yaml, and jupyterhub.singleuser.image in staging/prod.yaml, spawning in to the hub fails.

i'll address this in a later commit.

[shaneknapp]

ok, this is better (and basically works as advertised), but the logic around setting images is... wonky AF. i'm gonna take a quick break and think about what i can do to refactor/clean it up.

[shaneknapp]

ok, this is better (and basically works as advertised), but the logic around setting images is... wonky AF. i'm gonna take a quick break and think about what i can do to refactor/clean it up.

by deleting the wonky logic, and just letting help and jupyterhub figure things out, we have a much easier tool to maintain.

[shaneknapp]

still remaining TODO:

• check that `jupyterhub.singleuser.image.{name|tag} are both present and fail if missing in at least one config

[ryanlovett]

Fwiw, if the admin doesn't specify them, the chart falls back to defaults.

https://github.com/jupyterhub/zero-to-jupyterhub-k8s/blob/main/images/singleuser-sample/README.md

[shaneknapp]

Fwiw, if the admin doesn't specify them, the chart falls back to defaults.

https://github.com/jupyterhub/zero-to-jupyterhub-k8s/blob/main/images/singleuser-sample/README.md

odd, it failed to launch a notebook for me when i tried this, but the possibility of PEBKAC exists. i'll try again...

[shaneknapp]

Fwiw, if the admin doesn't specify them, the chart falls back to defaults.
https://github.com/jupyterhub/zero-to-jupyterhub-k8s/blob/main/images/singleuser-sample/README.md

odd, it failed to launch a notebook for me when i tried this, but the possibility of PEBKAC exists. i'll try again...

yep. PEBKAC. it's indeed using the default/sample image. i will still check for this as it's not exactly the behavior that we want.