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.

Solution 1:

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.

Solution 2:

I was getting the same nginx error and also there was no information in uwsgi log. The problem was that in some cases the application was not consuming the whole request body as advised in http://uwsgi-docs.readthedocs.org/en/latest/ThingsToKnow.html:

If an HTTP request has a body (like a POST request generated by a form), you have to read (consume) it in your application. If you do not do this, the communication socket with your webserver may be clobbered. If you are lazy you can use the post-buffering option that will automatically read data for you. For Rack applications this is automatically enabled.

Of course, this is not a problem in your case, but it may be useful for others who are getting the same nginx error.

Solution 3:

We just need to increase the attribute "output_buffering" value, in php.ini, to a greater value like 65535 or another appropriate value.