Why would TLJH time out?

TLJH is awesome. It solves one of my persistent problems of needing a way to get up and running in a commercial cloud environment quickly and consistently. So, I have an instance of TLJH installed in GCP. Installation was breeze – thanks for the detailed instructions! But the server keeps timing out. That is, if I don’t interact with the UI on a regular basis (e.g., let a long-running process of 60 minutes or so run its course while I do something else), it times out and shuts the server down. When I come back, I get an error message and have to refresh and restart the server. Which brings me to the questions in my title: why would TLJH ever time out? I can understand why you would want to time-out on a system that scales up and down (e.g., on Kubernetes), but in this case, the computational resources are fixed, so really time-outs should never happen (or am I missing something?). Alternatively, is there a way to configure it so that it never times out? As always, thanks for all your work!

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Hi,

Unless you changed it, the default behaviour in TLJH is to cull idle servers after 10 minutes. You should see if this is happening by inspecting /var/log/syslog. A check for idle servers happens every 60 seconds (by default), as shown by messages of the type:

200 GET /hub/api/users (cull-idle@127.0.0.1) 21.34ms

and the culling itself, after 600 seconds:

cull_idle_servers:154] Culling server (inactive for 00:10:35)

I’m not sure exactly how “inactive” is defined: it seems that servers can be culled even if the kernel is active but it is not writing to standard out (but this behaviour doesn’t seem to be 100% reproducible so perhaps it depends on other factors. If someone could clarify that would be great.).

You can turn off culling through the tljh-config config tool, as described here:

http://tljh.jupyter.org/en/latest/topic/idle-culler.html

i.e.,

sudo tljh-config set services.cull.enabled False
sudo tljh-config reload

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Thanks! That makes sense. I guess that page also answers my original question: you want to cull idle servers so that different users of your TLJH won’t be hogging resources from each other. The default behavior assumes a somewhat different use-case than mine (naturally), which is that many different users will be logging into the hub at different times.

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