I'm running a Django app on Apache 2.4.7 with mod_wsgi 3.4. The whole setup is on an EC2 ubuntu instance. Ever since I deployed the app, the server has gone down with 504/503 errors every few days with this message in the logs:
Script timed out before returning headers: wsgi.py
I've searched extensively but all I can conclude is I have a memory leak somewhere? I can't seem to figure out what's actually going wrong, since my Django install is pretty vanilla. This is the relevant part of my conf file:
WSGIScriptAlias / /home/ubuntu/projects/appname/app/app/app/wsgi.py WSGIDaemonProcess app python-path=/home/ubuntu/projects/appname/app user=ubuntu WSGIProcessGroup app WSGIApplicationGroup %{GLOBAL}
Could this be from some third party library? The only extras I have installed are ImageMagick and exiftool, the latter of which isn't being used. Is there anything else I can do to debug?
Does your application call out to any backend services?
If you are getting 503/504 and that message, then it would generally indicate that your code is either hanging on backend services or that your code is blocking indefinitely on thread locks.
So basically all request threads become busy and get used up.
If they didn't provide such an ancient version of mod_wsgi then newer versions do at least have better options to combat this sort of problem in your application and recover automatically, plus log information to help you work out why.
For such an old version, you can set 'inactivity-timeout' option to WSGIDaemonProcess to '60' as a way of recovering, but this will also have the effect of restarting your application after 60 seconds if it wasn't receiving any requests as well, which may in itself not be ideal for some apps. In newer versions the inactivity timeout is separated from the concept of a request timeout.
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