When debugging issues with a JupyterHub, admins often have to look at the log file to see what is going on. It can be very helpful to know what log messages mean, as they can sometimes mislead just as easily as they inform. I’ve started a documentation page adding common log messages emitted by JupyterHub, and what they mean. You can see the rendered output here: Common log messages emitted by JupyterHub — JupyterHub 2.2.0 documentation.
Would love for more PRs adding other log messages!