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When debugging errors and outages, looking at the logs emitted by JupyterHub is very helpful. This document tries to document some common log messages, and what they mean. I currently added just one log message, but we can add more over time. Ref https://github.com/2i2c-org/infrastructure/issues/1081 where this would've been useful troubleshooting
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Common log messages emitted by JupyterHub
When debugging errors and outages, looking at the logs emitted by JupyterHub is very helpful. This document tries to document some common log messages, and what they mean.
Failing suspected API request to not-running server
Your logs might be littered with lines that might look slightly scary
[W 2022-03-10 17:25:19.774 JupyterHub base:1349] Failing suspected API request to not-running server: /hub/user/<user-name>/api/metrics/v1
However, what this most likely means is that the user's server has stopped running but they still have a browser tab open. This is extremely common - for example, you might have 3 tabs open, and shut your server down via one. Or you closed your laptop, your server was culled for inactivity, and then you reopen your laptop again! The client side code (JupyterLab, Classic Notebook, etc) does not know yet that the server is dead, and continues to make some API requests. JupyterHub's architecture means that the proxy routes all requests that don't go to a running user server to the hub process itself. The hub process then explicitly returns a failure response, so the client knows that the server is not running anymore. This is used by JupyterLab to tell you your server is not running anymore, and offer you the option to let you restart it.
Most commonly, you'll see this in reference to the /api/metrics/v1
URL, used by jupyter-resource-usage.
So for the most part, this log line is pretty benign!