Nginx uwsgi (104: Connection reset by peer) while reading response header from upstream
Environment is Nginx + uwsgi.
Getting a 502 bad gateway error from Nginx on certain GET requests. Seems to be related to the length of the URL. In our particular case, it was a long list of GET parameters. Shorten the GET parameters and no 502 error.
From the nginx/error.log
[error] 22113#0: *1 recv() failed (104: Connection reset by peer) while reading response header from upstream, client: 192.168.1.100, server: server.domain.com, request: "GET <long_url_here>"
No information in the uwsgi error log.
Answer
After spending a lot of time on this, I finally figured it out. There are many references to Nginx and connection reset by peer. Most of them seemed to be related to PHP. I couldn't find an answer that was specific to Nginx and uwsgi.
I finally found a reference to fastcgi and a 502 bad gateway error (https://support.plesk.com/hc/en-us/articles/213903705). That lead me to look for a buffer size limit in the uwsgi configuration which exists as buffer-size. The default value is 4096. From the documentation, it says:
If you plan to receive big requests with lots of headers you can increase this value up to 64k (65535).
There are many ways to configure uwsgi, I happen to use a .ini file. So in my .ini file I tried:
buffer-size=65535
This fixed the problem. You can adjust that to taste. Maybe start with the max and work back until you have an acceptable value, or just leave it at the max.
This was frustrating to track down because there was no error on the uwsgi side of things.