Default to JupyterLab single document mode (/doc)

Proposed change

Switch the default repo2docker interface from jupyter-notebook to JupyterLab’s single document mode.

I’d like to gauge everyone’s feelings on if/when we’d make the switch.

Background

The trigger for this comes from the decision to switch Z2JH to JupyterLab: https://github.com/jupyterhub/zero-to-jupyterhub-k8s/issues/776#issuecomment-797276517. I asked whether we could change Z2JH to not set singleuser.cmd and instead default to whatever the default entrypoint/command is in the Docker image and instead change the default in the base docker-stacks images https://github.com/jupyterhub/zero-to-jupyterhub-k8s/issues/776#issuecomment-804063583, an advantage being we would no longer ignore the default start-up scripts that lead to problems such as https://discourse.jupyter.org/t/pyspark-library-is-missing-from-jupyter-pyspark-notebook-when-running-with-jupyterhub-zero-to-jupyterhub-k8s/8450/2, and also backwards compatibility would hopefully be easier to handle.

@parente pointed me to an existing docker-stacks discussion on switching to JupyterLab https://github.com/jupyter/docker-stacks/issues/1217 where one of the suggestions is to wait for other projects such as Z2JH and BinderHub (i.e. repo2docker) to switch. What does everyone think? If you can envisage switching R2D in the next few months then it might make sense to hold off on the Z2JH switch, and co-ordinate with docker-stacks instead to switch everything in one go. On the other hand if it’s longer then we should probably figure out how to switch Z2JH and ensure older images continue to work.

[SylvainCorlay]

Use https://mybinder.org/v2/gh/org/repo/HEAD to launch it and that this will start classic notebook

We could have a v3…

[minrk]

I think we should make this switch now. Summarizing the separate transitions we can make from discussion in the meeting and pr:

1. default UI to lab in repo2docker (NotebookApp.default_url)
2. default UI (and filepath) to lab in binderhub (URL construction, as in https://github.com/jupyterhub/binderhub/pull/1288)
3. switch server to jupyter_server (i.e. switch command to jupyter lab)

Switching UI in repo2docker and binderhub can reasonably be taken at the same time, but technically they are separate as BinderHub has full control over what URLs we redirect to (and with filepath, is fully overridden).

Personally, I think it’s appropriate to switch default UI today. This can be done entirely on mybinder.org as in https://github.com/jupyterhub/binderhub/pull/1288, or coordinated in both repo2docker and binderhub. The situation with lab and notebook only reverses: this only changes the default and is overridden easily with urlpath.

The server switch is a bigger deal, both because it’s likely more disruptive (presumably there will be compatibility issues with server extensions - how many server extensions are used on Binder?), and because it’s much harder to opt out on Binder (must specify the extreme override start command)