For a project, I created a prerender docker image after modifying the codes from prerender.io. I use systemd to run the docker container. It works fine in local machine and on one of the QA server, but the same image only returns 504 on a new QA server.
I checked the service log on the new QA and it shows 'response not sent for '.
After comparing the log between the old and new QA, I noticed that both services were able to get the index.html and other UI files but the service on the new QA did not make further ajax calls to the back-end. Instead, after fetching the front-end files, it logs 'response not sent for ' and then 'page timed out ' and 'parse html timed out ' and finally 'got 504 in 65230ms for ' (after adjusted the page load timeout).
There is an Nginx proxy listening to 80 and 443. I checked the firewall settings and 80 and 443 are allowed.
I am seeking for advice on where I should check with the 'response not sent' and 504 message.