upstream sent too big header while reading response header from upstream

Question

I am getting these kind of errors:

2014/05/24 11:49:06 [error] 8376#0: *54031 upstream sent too big header while reading response header from upstream

Answer 1

upstream sent too big header while reading response header from upstream is nginx's generic way of saying "I don't like what I'm seeing"

1. Your upstream server thread crashed
2. The upstream server sent an invalid header back
3. The Notice/Warnings sent back from STDERR overflowed their buffer and both it and STDOUT were closed

3: Look at the error logs above the message, is it streaming with logged lines preceding the message? PHP message: PHP Notice: Undefined index: Example snippet from a loop my log file:

2015/11/23 10:30:02 [error] 32451#0: *580927 FastCGI sent in stderr: "PHP message: PHP Notice:  Undefined index: Firstname in /srv/www/classes/data_convert.php on line 1090
PHP message: PHP Notice:  Undefined index: Lastname in /srv/www/classes/data_convert.php on line 1090
... // 20 lines of same
PHP message: PHP Notice:  Undefined index: Firstname in /srv/www/classes/data_convert.php on line 1090
PHP message: PHP Notice:  Undefined index: Lastname in /srv/www/classes/data_convert.php on line 1090
PHP message: PHP Notice:  Undef
2015/11/23 10:30:02 [error] 32451#0: *580927 FastCGI sent in stderr: "ta_convert.php on line 1090
PHP message: PHP Notice:  Undefined index: Firstname

you can see in the 3rd line from the bottom that the buffer limit was hit, broke, and the next thread wrote in over it. Nginx then closed the connection and returned 502 to the client.

2: log all the headers sent per request, review them and make sure they conform to standards (nginx does not permit anything older than 24 hours to delete/expire a cookie, sending invalid content length because error messages were buffered before the content counted...). getallheaders function call can usually help out in abstracted code situations php get all headers

examples include:

<?php
//expire cookie
setcookie ( 'bookmark', '', strtotime('2012-01-01 00:00:00') );
// nginx will refuse this header response, too far past to accept
....
?>

and this:

<?php
header('Content-type: image/jpg');
?>

<?php   //a space was injected into the output above this line
header('Content-length: ' . filesize('image.jpg') );
echo file_get_contents('image.jpg');
// error! the response is now 1-byte longer than header!!
?>

1: verify, or make a script log, to ensure your thread is reaching the correct end point and not exiting before completion.

Answer 2

We ended up realising that our one server that was experiencing this had busted fpm config resulting in php errors/warnings/notices that'd normally be logged to disk were being sent over the FCGI socket. It looks like there's a parsing bug when part of the header gets split across the buffer chunks.

So setting php_admin_value[error_log] to something actually writeable and restarting php-fpm was enough to fix the problem.

We could reproduce the problem with a smaller script:

<?php
for ($i = 0; $i<$_GET['iterations']; $i++)
    error_log(str_pad("a", $_GET['size'], "a"));
echo "got here\n";

Raising the buffers made the 502s harder to hit but not impossible, e.g native:

bash-4.1# for it in {30..200..3}; do for size in {100..250..3}; do echo "size=$size iterations=$it $(curl -sv "http://localhost/debug.php?size=$size&iterations=$it" 2>&1 | egrep '^< HTTP')"; done; done | grep 502 | head
size=121 iterations=30 < HTTP/1.1 502 Bad Gateway
size=109 iterations=33 < HTTP/1.1 502 Bad Gateway
size=232 iterations=33 < HTTP/1.1 502 Bad Gateway
size=241 iterations=48 < HTTP/1.1 502 Bad Gateway
size=145 iterations=51 < HTTP/1.1 502 Bad Gateway
size=226 iterations=51 < HTTP/1.1 502 Bad Gateway
size=190 iterations=60 < HTTP/1.1 502 Bad Gateway
size=115 iterations=63 < HTTP/1.1 502 Bad Gateway
size=109 iterations=66 < HTTP/1.1 502 Bad Gateway
size=163 iterations=69 < HTTP/1.1 502 Bad Gateway
[... there would be more here, but I piped through head ...]

fastcgi_buffers 16 16k; fastcgi_buffer_size 32k;:

bash-4.1# for it in {30..200..3}; do for size in {100..250..3}; do echo "size=$size iterations=$it $(curl -sv "http://localhost/debug.php?size=$size&iterations=$it" 2>&1 | egrep '^< HTTP')"; done; done | grep 502 | head
size=223 iterations=69 < HTTP/1.1 502 Bad Gateway
size=184 iterations=165 < HTTP/1.1 502 Bad Gateway
size=151 iterations=198 < HTTP/1.1 502 Bad Gateway

So I believe the correct answer is: fix your fpm config so it logs errors to disk.

Answer 3

This is still the highest SO-question on Google when searching for this error, so let's bump it.

When getting this error and not wanting to deep-dive into the NGINX settings immediately, you might want to check your outputs to the debug console. In my case I was outputting loads of text to the FirePHP / Chromelogger console, and since this is all sent as a header, it was causing the overflow.

It might not be needed to change the webserver settings if this error is caused by just sending insane amounts of log messages.

Answer 4

Add the following to your conf file

fastcgi_buffers 16 16k; 
fastcgi_buffer_size 32k;

Answer 5

Plesk instructions

In Plesk 12, I had nginx running as a reverse proxy (which I think is the default). So the current top answer doesn't work as nginx is also being run as a proxy.

I went to Subscriptions | [subscription domain] | Websites & Domains (tab) | [Virtual Host domain] | Web Server Settings.

Then at the bottom of that page you can set the Additional nginx directives which I set to be a combination of the top two answers here:

fastcgi_buffers 16 16k;
fastcgi_buffer_size 32k;
proxy_buffer_size   128k;
proxy_buffers   4 256k;
proxy_busy_buffers_size   256k;

Answer 6

If you're using Symfony framework: Before messing with Nginx config, try to disable ChromePHP first.

1 - Open app/config/config_dev.yml

2 - Comment these lines:

#chromephp:
    #type:   chromephp
    #level:  info

ChromePHP pack the debug info json-encoded in the X-ChromePhp-Data header, which is too big for the default config of nginx with fastcgi.

Source: https://github.com/symfony/symfony/issues/8413#issuecomment-20412848