Server response gets cut off half way through

I had the same problem:

Nginx cut off some responses from the FastCGI backend. For example, I couldn't generate a proper SQL backup from PhpMyAdmin. I checked the logs and found this:

2012/10/15 02:28:14 [crit] 16443#0: *14534527 open() "/usr/local/nginx/fastcgi_temp/4/81/0000004814" failed (13: Permission denied) while reading upstream, client: *, server: , request: "POST / HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "", referrer: "http://*/server_export.php?token=**"

All I had to do to fix it was to give proper permissions to the /usr/local/nginx/fastcgi_temp folder, as well as client_body_temp.

Fixed!

Thanks a lot samvermette, your Question & Answer put me on the right track.

I had similar problem with cutting response from server.

It happened only when I added json header before returning response header('Content-type: application/json');

In my case gzip caused the issue.

I solved it by specifying gzip_types in nginx.conf and adding application/json to list before turning on gzip:

gzip_types text/plain text/html text/css application/x-javascript text/xml application/xml application/xml+rss text/javascript application/json;
gzip on;

Looked up my nginx error.log file and found the following:

13870 open() "/var/lib/nginx/tmp/proxy/9/00/0000000009" failed (13: Permission denied) while reading upstream...

Looks like nginx's proxy was trying to save the response content (passed in by thin) to a file. It only does so when the response size exceeds proxy_buffers (64kb by default on 64 bits platform). So in the end the bug was connected to my request response size.

I ended fixing my issue by setting proxy_buffering to off in my nginx config file, instead of upping proxy_buffers or fixing the file permission issue.

Still not sure about the purpose of nginx's buffer. I'd appreciate if anyone could add up on that. Is disabling the buffering completely a bad idea?