Pre-pull user images at node startup

Image pre-pulling before user arrival is not a feature enabled by default on the hubs, because it comes with an increase in cloud costs. However, there are situations like exams, events, or even just a hub with large images when users need faster startup times. If communities agreed to the cost tradeoff, then this feature should be enabled.

More about it at https://z2jh.jupyter.org/en/stable/administrator/optimization.html#pulling-images-before-users-arrive

Enable continuous-image-puller

The following config will pre-pull all images specified through profile lists or directly, on all nodes, when they start up.

jupyterhub:
  prePuller:
    continuous:
      enabled: true

Explicitly specify extra images to pre-pull

You can also specify additional images to pre-pull on the nodes. This can be either images used by init containers or extra containers.

Example:

jupyterhub:
  prePuller:
    continuous:
      enabled: true
      extraImages:
        nbgitpuller:
          name: public.ecr.aws/nasa-veda/jupyterhub-gitpuller-init
          tag: 97eb45f9d23b128aff810e45911857d5cffd05c2
        s3fs:
          name: mas.dit.maap-project.org/root/che-sidecar-s3fs
          tag: 2i2c # This is a mutable tag, so may trigger re-pulls