This issue happens on a pure PHP files served by Nginx & PHP-FPM. I've stumbled upon this issue while developing my website using Symfony but the problematic content length range is 3702-15965 for that (I wonder why it's different than vanilla PHP).
What I've tried so far:
- Timeout duration is 15 seconds but I've tried increasing it to 300 seconds and it still timeouts. So I'm guessing it's infinite loopy thing.
- It doesn't look like it's resource related because it works even if content length is 5 million characters.
- Created various tests with different characters to see if I can cause changes to the problematic content length range. Answer is no, range stayed same for all my tests.
- I have tried disabling gzip. It didn't change the length range but the response changed. Gzip enabled response: "upstream request timeout" | Gzip disabled response: Completely blank
Notes:
- This issue doesn't exist on my localhost.
- It rarely opens the page normally. I can't reproduce this consistently.
- There are no errors in Nginx, PHP or GCR logs besides the "request timed out" lines.
Any help is appreciated. Thanks.
Funnily enough, I've solved the issue while writing the question. Adding fastcgi_buffering off; to Nginx config fixes the issue.
But I still don't understand what was the problem and why disabling buffering fixed it. So if anyone can explain it I don't mind marking that answer as solution.