Server hangs with 2 parallel requests

[phackwer]

Hi. W using are e the Phusion/Passenger docker container (https://github.com/phusion/passenger-docker) and I'm having the most unusual problem here: when running a docker container locally (as development) that has IMGKit, my code runs smooth, and generates the images properly. But when we go to the QA server, the QA hangs in the second request. wkhtmltoimage seems to get stuck, with no hope to ever come back. If I go into the docker container and kill the process manually (killall wkhtmltoimage-amd64) rails start responding other requests.

Now: what is really bizarre: if I call the endpoints that generate the images directly from my browser, al go, all normal... There is nothing special on the headers, actually it's a pretty standard get with the token in the URL, so there should be no problem at all with it!

Also, the same code that generates the images is used in a different part of our system (as we created it as a concern to be used on different controllers), and they are all working fine!!!