[MRG] Improve docs on Dockerfile escape hatch

[MattF-NSIDC]

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I was struggling to find how to get the generated Dockerfile contents. When I found it, I thought I'd open a PR to add a link from the first place I looked for the next person who struggles :)

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[MattF-NSIDC]

I experienced some unexpected behavior and added a warning to the docs :point_up:

[MattF-NSIDC]

I feel like more documentation is needed. When I create a Dockerfile following these instructions and attempt to build, there are errors because the Dockerfile references paths that aren't in the build context:

Step 26/60 : COPY --chown=1002:1002 build_script_files/-2fhome-2fmfisher-2f-2eminiconda3-2fenvs-2frepo2docker-2flib-2fpython3-2e11-2fsite-2dpackages-2frepo2docker-2fbuildpacks-2fconda-2factivate-2dconda-2esh-cf5cc0 /etc/profile.d/activate-conda.sh
COPY failed: file not found in build context or excluded by .dockerignore: stat build_script_files/-2fhome-2fmfisher-2f-2eminiconda3-2fenvs-2frepo2docker-2flib-2fpython3-2e11-2fsite-2dpackages-2frepo2docker-2fbuildpacks-2fconda-2factivate-2dconda-2esh-cf5cc0: file does not exist(repo2docker)

When I remove those steps, later steps fail because mamba and conda are both unavailable. What else can I do to document the process of switching from a non-Dockerfile config to a Dockerfile-based config?

[manics]

The debug output is just for debugging, it's not intended to be buildable since you also need the full context that's created on the fly, and I don't think we should recommend it as a way to create a Dockerfile.

I've got a playground/proof-of-concept in https://github.com/manics/repo2shellscript if you're interested in seeing the full complexity.

[MattF-NSIDC]

Thanks @manics! Is there anything that can be documented about migrating from a config-file based build to a Dockerfile-based build? Does repo2docker provide any value add for that use case? I'm struggling with a build that has broken man pages, and I'm not seeing a repo2docker path to fixing it right now (since I think I need to do stuff as root to fix the issue).

[MattF-NSIDC]

https://github.com/jupyterhub/repo2docker/issues/700

[MattF-NSIDC]

Here's how I solved my problem: https://github.com/CryoInTheCloud/hub-image/pull/65

As you know, I totally missed the "Can I use repo2docker to bootstrap my own Dockerfile?" FAQ on my first time through :laughing: I've added a link to it where I would have seen it my first time through and replaced my bad suggestions with hopefully better ones, in addition to a new FAQ to resolve the specific problem with man pages.