How to solve Canvas overload Issue: This website is under heavy load (queue full)

Published: 23 June, 2022

If you are the self-hosted Open source Canvas LMS administrator, you would get this error message from your end users: This website is under heavy load (queue full). We need to think about why this happened? Here is the clue and solution you would try.

Canvas LMS is using the Passenger module for the Apache HTTP engine. You need to think about the limitation of the request queue when the Canvas LMS is crashed with an error message about heavy load and queue full. Here is the Passenger official documentation about the PassengerMaxRequestQueueSize configuration:


Now let's change the PassengerMaxRequestQueueSize setting of the Passenger module.

$ cd /etc/apache2/mods-enabled
$ nano passenger.conf

In the section, add the PassengerMaxRequestQueueSize:

  PassengerRoot /usr/lib/ruby/vendor_ruby/phusion_passenger/locations.ini
  PassengerDefaultRuby /usr/bin/passenger_free_ruby
  PassengerDefaultUser canvas
  PassengerMaxRequestQueueSize 700

Save changes and restart the services:

sudo /etc/init.d/canvas_init restart
sudo /data/canvas/script/delayed_job restart
sudo /etc/init.d/apache2 restart


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