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cul-2016 / quiz

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Not possible to log in #717

Open stianr opened 5 years ago

stianr commented 5 years ago

Lots of students in a current lecture are unable to log in to Quodl. I am similarly unable to log in to see what is wrong. If I go to the login page and try to log in with the correct credentials, I'm just returned to the login page with the fields cleared. There was also a lot of activity today when the quiz was run, relative to previous weeks. The student numbers were lower than in previous weeks, so I'm not sure why this happened.

(And obviously I can't log in to try to identify the problem by looking at the user data...)

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stianr commented 5 years ago

Issue appear to be cookie based. If I log in using a private window it works fine.

EDIT: Not clear if this is the case, as I can also now log in using normal browser window.

stianr commented 5 years ago

Problem seems to have resolved itself, but it has caused a lot of disruption to a lecture, so needs to be investigated.

iteles commented 5 years ago

We'll look into this @stianr

Danwhy commented 5 years ago

Hi @stianr, based on what you said about it eventually fixing itself and from what I've seen in the logs, it looks like this was just caused by an overload of too many people trying to log on at the same time. I'm not entirely sure why this would happen when the student count was lower than normal, but perhaps it was just a unlucky case of everybody trying to access it at the exact same time.

The only suggestion i can really make is the same as before around looking into optimising the websockets: https://github.com/cul-2016/quiz/issues/553#issuecomment-428998385

stianr commented 5 years ago

Thanks for looking into this @Danwhy. Makes sense that it looks like it got overloaded. I'm just concerned about why. Agree it might be partly that students tried to log in at the same time, but from the logs it looked like there was a sustained 100-150 requests per second for ten minutes. This is way more than we usually see, so I want to understand what might have been different this time. I guess it could be that an inital spike overloaded the system and prevented new logins and then all the excess requests were students trying to log in again (but that's a lot of requests if they're coming manually). Or that network problems led to excessive new requests.

We'll give it a go and see if the problem arises again on Monday (I've said I'll go along so will be able to report back first hand). That may help work out whether it's a transient issue or not.