Nginx + PHP FASTCGI FAILS - how to debug?

Question

I have a server on AMAZON EC2 running Nginx +PHP with PHP FASTCGI via port 9000.

The server runs fine for a few minutes and after a while (several thousands of hits in this case) FastCGI Dies and Nginx returns 502 Error.

Nginx log shows

 2010/01/12 16:49:24 [error] 1093#0: *9965 connect() failed (111: Connection refused) while connecting to upstream, client: 79.180.27.241, server: localhost, request: "GET /data.php?data=7781 HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "site1.mysite.com", referrer: "http://www.othersite.com/subc.asp?t=10"

How can I debug what is causing FastCGI to die?

Answer 1

I realize that the OP may have moved on by now, but if somebody came here with the same problem, I hope this helps.

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In a default setup, NGINX runs as the user "nobody" whereas spawn-fcgi spawns php-cgi children as the user "root". So, NGINX is unable to connect to fastcgi://127.0.0.1:9000 with it's current permissions. All you have to do is change the spawn-fcgi command a little bit to fix this.

spawn-fcgi -a 127.0.0.1 -p 9000 -f /usr/bin/php-cgi -C 5 -U nobody

Or you could use a UNIX socket (I prefer this method)

spawn-fcgi -s /var/run/fcgi.sock -f /usr/bin/php-cgi -C 5 -U nobody

And change your fastcgi_pass in nginx.conf to this:

...
 location ~ \.php$ {
        fastcgi_pass   unix:/var/run/fcgi.sock;
        fastcgi_index  index.php;
        include        fastcgi_params;
        fastcgi_param SCRIPT_FILENAME /usr/local/nginx/html$fastcgi_script_$
    }
...

Answer 2

You can start by examining what PHP prints on standard error when it dies. If that sheds no light on the matter, then it might be enlightening to hook up a strace to the PHP processes and watch them do their thing, and then look at the last things it does. Running your FCGI processes under a competent process monitoring framework such as daemontools is also a good idea -- it's how I run all my PHP processes under nginx.