Support custom culling logic through hooks (like Spawner's pre_spawn_hook etc)

[consideRatio]

Proposed change

Just like the JupyterHub Spawner and JupyterHub Authenticator classes have various hooks that can be used to take various actions, I think it could make sense to expose some hooks to the JupyterHub idle culler.

I don't have a need for this personally, but reflecting on #24 adding --cull-admin-users I felt it could be relevant to allow for some custom logic to play a role in the decision to cull a user server or a JupyterHub user identity.

Who would use this feature?

Anyone that would want to make culling decisions based on user state, such as belonging to a certain group or similar.

(Optional): Suggest a solution

We add hooks that we can configure using traitlets that are given some information of relevance and where their return value could influence culling decisions. I'm not sure what hooks would make sense.

Action points

1. Brainstorm hooks of relevance to address a various needs
2. Suggest a reduced set of hooks that together can address most needs
3. Make a decision if we should implement such set of hooks in this project
4. Add a PR with hooks documented and with some tests

Related issues / PRs

• Option to send warning email before deleting user #4, Adding the option to delete persisted user data as well. #8, How configurable should the culler be? #9, Support custom culling logic through hooks (like Spawner's pre_spawn_hook etc) #25

[Zhell1]

found this issue while looking for a similar solution to KubeSpawner's PreStop hook, actually needing this for the project I am working on right now.

[rccern]

Hi, I have a similar use case:

In our Jupyterhub deployment we have the possibility of assigning users to nodes with GPU, which are a "scarce" resource. For this reason, we would like to have different timeouts depending on which resources the users have booked, e.g. letting sessions expire after 2h since last_activity for nodes with GPUs and 6h for nodes using only CPU.

I was thinking about customizing the should_cull https://github.com/jupyterhub/jupyterhub-idle-culler/blob/main/jupyterhub_idle_culler/__init__.py#L238 with a configurable callable which takes as inputs the user and the server objects and returns a boolean. Does it make any sense? I can work on a PR in case you find it useful

[danilopeixoto]

Hi,

We would like to cull servers based on profile. That will be great!
For example, delete the server only if it is a minimal notebook profile.

[marty90]

I have the exact case of @rccern. We would like to cull pods for some JHub profiles faster. Is there any workaround for this?

[dasantonym]

+1 from me as well! Would be great to have this functionality.