Give users feedback on image transfer progress

[betatim]

Transferring the container image takes a long time during the launch of an already built repository.

Is it possible to show the size of the image and maybe even how much progress we have made fetching it?

This came up in jupyterhub/repo2docker#686 (comment)

[consideRatio]

Hmmmm hmmmm this would be awesome! The question is now planted in my mind, I have no answer about if it would be possible though.

[sgibson91]

I thought about the little arrows ==> you get when running docker push. That might be one way to "fool" the users that something is happening if we can create such a progress bar?

[betatim]

#886 is (only) about what happens during a launch.

Image transfer happens at the end of a build (to the registry) and at launch time (from registry to the node) though. During launch I don't think we get access to the progress of the image pull, during the push we know what % has been transferred of each layer.

[minrk]

repo2docker passes us progress info in the log event. So each "Pushing image..." event actually contains all the layer progress info in metadata. We could be rendering this.

Alternately, we could switch the repo2docker events to be tqdm-rendered terminal progress bars instead of higher-level push metadata to be rendered by the client.

[minrk]

FWIW, this is what a push event looks like:

{
  "message": "Pushing image\n",
  "progress": {
    "9ef4a26e7b8c": "Pushed",
    "69ac14f57ddb": "Pushed",
    "251480c8f99f": "Pushed",
    "63f60c84dfa3": "Pushed",
    "db13a1a23932": {
      "current": 117909504,
      "total": 758965327
    },
    "8fdb014353db": {
      "current": 6656,
      "total": 71
    },
    "bcd062287812": {
      "current": 2560
    },
    "79c7f8114a96": {
      "current": 4608,
      "total": 2454
    },
    "3502237e46ed": {
      "current": 3584,
      "total": 772
    },
    "2efde80b98e5": "Waiting",
    "d38b6fe234e0": "Waiting",
    "9a6b400e9755": "Waiting",
    "f50c2143d6ab": "Preparing",
    "c4e3746c2dbb": "Waiting",
    "f5675e8b8787": "Waiting",
    "adda4de99b3d": "Waiting",
    "3a034154b7b6": "Waiting",
    "0712b41b4157": "Waiting",
    "a2178543b63f": "Waiting",
    "75e70aa52609": "Preparing",
    "dda151859818": "Waiting",
    "fbd2732ad777": "Waiting",
    "ba9de9d8475e": "Waiting"
  },
  "phase": "pushing"
}

I don't know what all the possible string state values are. Interestingly, current doesn't appear to be on the same scale as total for in-progress layers. Maybe a bug in docker engine?