Add base_url capability to tljh-config

[jeanmarcalkazzi]

This pull request:

• fixes tljh-config reload should use base url #616
• fixes Allow running TLJH under a URL prefix #216
• fixes Is possible to make the-littlest-jupyterhub run in other port/url ? #426

A function update_base_url now sets c.JupyterHub.base_url to the requested value, and correctly checks for it during the check_hub_ready function.

• Add / update documentation
• Add tests

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[jeanmarcalkazzi]

@GeorgianaElena here's the fix for @ikhoury 's issue #616
Some tests are failing here due to broken master.

[GeorgianaElena]

Thanks for working on this, @jeanmarcalkazzi, it looks great 🎉
What do you think about adding a small integration test in test_hub.py to check if a user can login using the new hub url and can start its server?

Update: Don't worry about the failing upgrade test, I don't think it's related to this PR. There is a memory limit issue that keeps coming back.

Update2: @jeanmarcalkazzi, I edited your initial comment, so that when this PR is merged, all the related issues to be closed. Hope that's ok.

[jeanmarcalkazzi]

I will do so in the next few days!
Any specific requirement/aspect to keep in mind for testing?
@GeorgianaElena

[GeorgianaElena]

The test should be similar with what happens along these lines: https://github.com/jupyterhub/the-littlest-jupyterhub/blob/master/integration-tests/test_hub.py#L27-L41, setting in addition the base_url.
One thing to keep in mind, all the tests in test_hub.py run in the same container, so I'd suggest unsetting the new base_url after the user server started, so that the other tests won't fail.

[jeanmarcalkazzi]

CircleCI output:

WARNING: Your kernel does not support swap limit capabilities or the cgroup is not mounted. Memory limited without swap.
b84998b985cfd0e8f45141c9dd0a599ec54c6e313430295724a722be44e0d0de
^@^@Checking if TLJH is already installed...
Setting up hub environment
Installed python & virtual environment
Set up hub virtual environment
Setting up TLJH installer...
Upgraded pip
Setup tljh package
Starting TLJH installer...
Granting passwordless sudo to JupyterHub admins...
Setting up user environment...
Downloading & setting up user environment...
Traceback (most recent call last):
  File "/usr/lib/python3.6/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/opt/tljh/hub/lib/python3.6/site-packages/tljh/installer.py", line 530, in <module>
    main()
  File "/opt/tljh/hub/lib/python3.6/site-packages/tljh/installer.py", line 502, in main
    ensure_user_environment(args.user_requirements_txt_url)
  File "/opt/tljh/hub/lib/python3.6/site-packages/tljh/installer.py", line 278, in ensure_user_environment
    'conda==' + conda_version
  File "/opt/tljh/hub/lib/python3.6/site-packages/tljh/conda.py", line 108, in ensure_conda_packages
    ] + packages).decode()
  File "/usr/lib/python3.6/subprocess.py", line 356, in check_output
    **kwargs).stdout
  File "/usr/lib/python3.6/subprocess.py", line 438, in run
    output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command '['/opt/tljh/user/bin/python', '-m', 'conda', 'install', '-c', 'conda-forge', '--json', '--prefix', '/opt/tljh/user', 'conda==4.8.1']' died with <Signals.SIGKILL: 9>.
Traceback (most recent call last):
  File ".circleci/integration-test.py", line 189, in <module>
    main()
  File ".circleci/integration-test.py", line 173, in main
    run_test(image_name, args.test_name, args.bootstrap_pip_spec, args.test_files, args.upgrade, args.installer_args)
  File ".circleci/integration-test.py", line 108, in run_test
    f'python3 /srv/src/bootstrap.py {installer_args}'
  File ".circleci/integration-test.py", line 71, in run_container_command
    ], check=True)
  File "/usr/lib/python3.6/subprocess.py", line 438, in run
    output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command '['docker', 'exec', '-it', 'basic-tests', '/bin/bash', '-c', 'python3 /srv/src/bootstrap.py ']' returned non-zero exit status 1.

Exited with code exit status 1
CircleCI received exit code 1

@GeorgianaElena I think this is related to the memory issue you mentioned.

[GeorgianaElena]

I believe you're right @jeanmarcalkazzi 😕 I will investigate this tomorrow. Thank you!

[jeanmarcalkazzi]

Changes done.
@GeorgianaElena let me know if I can help with the debugging of this memory issue!

[GeorgianaElena]

Hey @jeanmarcalkazzi 👋 The tests were fixed, so I've rebased the PR and now all the bots are happy and everything is green 🥳

I'll go ahead and merge this now. Thanks a lot for your work and patience 🌻

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