Nginx + FastCGI + C throws 502 Bad Gateway

Question

I'm trying to run an Nginx with FASTCgi to handle request through C app backend.

I'm using this tutorial: http://www.kutukupret.com/2010/08/20/nginx-fastcgi-hello-world-in-c/

My nginx configuration file:

server
  {
    listen 80;
    listen [::]:80 default ipv6only=on;

    server_name localhost;

    location /
    {
      fastcgi_pass   127.0.0.1:8000;

      fastcgi_param  GATEWAY_INTERFACE  CGI/1.1;
      fastcgi_param  SERVER_SOFTWARE    nginx;
      fastcgi_param  QUERY_STRING       $query_string;
      fastcgi_param  REQUEST_METHOD     $request_method;
      fastcgi_param  CONTENT_TYPE       $content_type;
      fastcgi_param  CONTENT_LENGTH     $content_length;
      fastcgi_param  SCRIPT_FILENAME    $document_root$fastcgi_script_name;
      fastcgi_param  SCRIPT_NAME        $fastcgi_script_name;
      fastcgi_param  REQUEST_URI        $request_uri;
      fastcgi_param  DOCUMENT_URI       $document_uri;
      fastcgi_param  DOCUMENT_ROOT      $document_root;
      fastcgi_param  SERVER_PROTOCOL    $server_protocol;
      fastcgi_param  REMOTE_ADDR        $remote_addr;
      fastcgi_param  REMOTE_PORT        $remote_port;
      fastcgi_param  SERVER_ADDR        $server_addr;
      fastcgi_param  SERVER_PORT        $server_port;
      fastcgi_param  SERVER_NAME        $server_name;
    }
  }

My C File "hello.c":

#include <fcgi_stdio.h>
int main( int argc, char *argv[] )
{
   while( FCGI_Accept() >= 0 ) {
      printf( "Content-Type: text/plainnn" );
      printf( "Hello world in Cn" );
   }
   return 0;
}

I compile the C file with the FastCGI dev kit and it generates a hello binary file.

Finally I run this line: spawn-fcgi -a 127.0.0.1 -p 8000 -n /var/www/example.com/bin/hello

But when I put in the browser http://localhost it throws a "502 Bad Gateway".

Can someone bring me some light?

Answer 1

Your printf line has errors -

printf( "Content-Type: text/plainnn" );

should be -

printf( "Content-Type: text/plain\r\n\r\n" );

Note the \r\n\r\n This is a mandatory separator between HTTP headers and the HTTP body.

Answer 2

I would advise to look at nginx error logs:

sudo tail -f /var/log/nginx/error.log

I was getting the same error, but with a C++ server which was using CppCMS library and a unix socket to communicate with nginx. From the error log I could see that there was a problem with the file permissions of the socket file:

2014/05/28 14:52:01 [crit] 1818#0: *172 connect() to unix:/tmp/fcgi-socket failed (13: Permission denied) while connecting to upstream, client: 127.0.0.1, server: localhost, request: "GET /server HTTP/1.1", upstream: "fastcgi://unix:/tmp/fcgi-socket:", host: "localhost:8080"

just setting them to 777 solved the issue for me.

Answer 3

Its look like your php5-fpm is not running om 8000 port as you included in nginx conf

fastcgi_pass   127.0.0.1:8000;

You can verify your php5-fpm is running on that port by using following commands

grep -Hr "8000" /etc/php5/fpm/pool.d

For setup php5-fpm on 8000 open following file and change listen to 8000 port

vim etc/php5/fpm/pool.d/www.conf

now search listen and replace it with following line

listen = 127.0.0.1:8000

Save the file and restart php5-fpm

Answer 4

I experienced the same error in the past. The configuration below worked for me.

location / {
    include fastcgi_params;
    fastcgi_pass  localhost:8000;
}