Giving hub.cl an upgrade

For a few years now we've been running hub.cl.cam.ac.uk, a Jupyterhub instance, for the first year course "Foundations of Computer Science". It serves as a hosting site for the lecture notes, which come in the form of Jupyter notebooks, and as a playground where students can try OCaml, and it also is used to run the assessed exercises that are a mandatory part of the course.

Since I spent some time setting it up back in 2018 or so, its aggregated some cruft over the years, and has also fallen somewhat behind the bleeding edge of the Jupyter software stack. So I thought this year, as I'm actually lecturing the course, I'd give it a bit of loving care and attention.

We were still on Jupyterhub 1.5.3 whereas the current release is 5.3.0 - so there was quite a bit of work to do. I brief play with putting things on the latest version seemed to break quite a lot of things, so I thought it might be better to go back to the drawing board and start the config again from scratch. So with some help from Claude, I've now managed to hugely simplify the whole config of Jupyterhub, and even given it a makeover to try to match the style of www.cst.cam.ac.uk as well. The improvements include:

• Using caddy as a reverse proxy for TLS termination, meaning I don't have to manually renew the letsencrypt cert every 3 months
• Unifying the configuration of the two container images used for students and instructors
• Upgrading to much newer jupyterhub, notebook and nbgrader images
• Simplifying the configuration required to make it work on a new server - persistent user directories are now docker volumes rather than bindmounts on the local filesystem
• Updating the authentication method to use Raven via OAuth2 rather than the unmaintained jupyterhub-raven-auth which I'd had to maintain a patch.
• Rebasing my patch to nbgrader to verify all of the output of the cells when grading answers

As ever, this took longer than I'd anticipated, but I'm mostly there now. There are a few more steps to try:

• trial the new patch for using ocaml-jupyter with OCaml 5.x
• see how to upgrade to notebook v7, as I've stuck with v6 in order to keep the extensions we're using going.