large_client_header_buffers: Custom error pages are not working

Tue Jun 5 09:34:10 UTC 2018

Hi there,
I'm using nginx nginx version 1.12.0 as a reverse proxy to my application
servers. 
I allow certain top level checks like header size and count to be done at
nginx level.

The server block looks like the following:

server {
listen            443 ssl default_server;
..
large_client_header_buffers 32 512;
..
  location / {
  ... 
  }

   error_page 400 /400.json;
   location = /400.json {
	root /etc/nginx/errors-files/;
	allow all;
	internal;
   }

}

Then I start testing the nginx with curl and adding a header of size 600
bytes. 
nginx promptly stops the request and dumps a default error page instead of
my custom error page.

<html>
<head><title>400 Request Header Or Cookie Too Large</title></head>
<body bgcolor="white">
<center><h1>400 Bad Request</h1></center>
<center>Request Header Or Cookie Too Large</center>
<hr><center>nginx</center>
</body>
</html>

How can I get a CUSTOM ERROR page for this situation working instead of the
default page.
Thanks
Cheers
prajos

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,280035,280035#msg-280035