log hook messages to stderr

[minrk]

Describe your changes

• use _log in run-hooks.sh, like start.sh (needs to redefine it for unnittests only, could split into a common utility file)
• _log writes to stderr instead of stdout for easier output capture (piping, etc.)

In general, it's a good practice to avoid logging to stdout, since it means you can't capture command output with pipes, e.g.

docker run --rm -it quay.io/jupyter/base-notebook conda env export > base-env.yml

because it will include the 'uid: 1000`, etc. messages.

Checklist (especially for first-time contributors)

• I have performed a self-review of my code
• If it is a core feature, I have added thorough tests
• I will try not to use force-push to make the review process easier for reviewers
• I have updated the documentation for significant changes

I looked through the tests, and it's tricky because the tests run with tty: true, in which case docker merges stdout and stderr, so can't test the splitting is correct. Running with tty: false, e.g. docker run --rm -i pwd > stdout.txt 2>stderr.txt does the right thing in a manual test. I'm just not 100% sure of the best way to add a test case for that with the current infrastructure.

[mathbunnyru]

I looked through the tests, and it's tricky because the tests run with tty: true, in which case docker merges stdout and stderr, so can't test the splitting is correct. Running with tty: false, e.g. docker run --rm -i pwd > stdout.txt 2>stderr.txt does the right thing in a manual test. I'm just not 100% sure of the best way to add a test case for that with the current infrastructure.

Hi @minrk, all our tests run fine with and without tty (I recently worked on that), but I enabled tty by default to have color logs and to spot errors easier.

The only exception where I had to disable it was here:

docker-stacks/tests/by_image/docker-stacks-foundation/test_user_options.py

Line 183 in 5b8d531

timeout=10, no_warnings=False, user="1010", command=["id"], tty=False

You can also disable it for your individual tests if needed.

[minrk]

Thanks! I added a way to split stdout and stderr and some tests to exercise this.

[mathbunnyru]

Overall, looks great, asked to change 2 small things.

[mathbunnyru]

🚀
Please, squash-merge when CI is green