Add feature to use unused autograder runs at midnight

[Ram-G]

#19, #35

Adds an endpoint under staff routes. This can be triggered by a cron script from the grader VM everyday, say, at 12:00:01 AM.

TODO: Needs testing. Need to verify that datetime usage is correct (do timezones mess with this somehow?)

[redsn0w422]

@shreyas208, @Ram-G status on this?

[nmagerko]

I'd like to close this unless there's some more work that will be done here. Thoughts?

[ayushr2]

From what it looks like, this exposes a new endpoint which we will need to hit externally.
Could we instead add a thread to the On-Demand app itself which acts as a scheduler? It sleeps until the next most recent task is due. We can wake it up to add a new task and it will go back to sleep for the most recent task. That way we can even have deadline AG runs on On-Demand as well.

[nmagerko]

I personally don't like the idea of getting the on-demand app involved in scheduling, but maybe others will find that appealing.

[bhuvy2]

Don’t know if I should put this here, but timezones do mess with this because of daylight savings

[Ram-G]

The idea of having it in an external endpoint and not baked into the app was that then we could control the runs without have to restart the on-demand app. As for the feature itself, ref some discussions on slack with @redsn0w422 and @shreyas208, I think we didn't come to a conclusion whether we want this feature at all. It's a nice-to-have but it encourages students to be lazier with using their runs.

@bhuvy2 I agree, I think daylight savings would mess with it. Reading up a bit about it, it seems using UTC time would fix that. I can do that if we want to merge this feature.

[bhuvy2]

I’d recommend using pytz and America/Chicago which will convert naive timezones into localized time zones. After, you can convert to UTC and schedule.

If you just use UTC to schedule, it won’t convert naive time zones to properly localized ones.

As for the scheduling questions, I wouldn’t recommend using cron because it is an anti-pattern. Any scheduling that contributes to application logic should be in the applications.

If we do go with scheduling baked into the flask app, APScheduler would be preferable (celery involves us setting up rabbitmq which is overkill)

[Xiangmingchen]

I'll close this since it's a very old PR and we are currently trying to incorporate APScheduler into our app and enable scheduling grading runs from on-demand. If we still want to implement this feature, we will use APScheduler instead.