nginx 502 bad gateway after ubuntu server restart

Question

I have a situation with an ubuntu server that is configured to run with nginx and fastcgi. The problem is that after a restart any request is giving 502 bad gateway in browser.

In error log the error looks like this:

 connect() to unix:/var/run/fastcgi.socket-4 failed (2: No such file or directory) while connecting to upstream

after I create the file manually (i do not know if this is correct) the error is changing to:

connect() to unix:/var/run/fastcgi.socket-4 failed (111: Connection refused) while connecting to upstream

nginx server has configuration settings for each website like this:

 location ~ \.php$ {
                        fastcgi_pass                    unix:/var/run/fastcgi.socket-4;
                        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_scr
                        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;
                        fastcgi_param   REDIRECT_STATUS         200;
                        fastcgi_index                   index.php;
                        fastcgi_intercept_errors        on;
                        }

Note that I am quite new to nginx, however I have experience and knowhow in apache and php.

Answer 1

The 502 bad gateway error means that the backend server (which is php in your case) is not functioning properly, and since it was related to a server restart, I guessed it would be related to it not starting on boot time.

Since I didn't know the service name, running sudo service --status-all lists all services on the system.

After finding the php service name which turned to be spawn-fcgi in your case, you can start it using

sudo service spawn-fcgi start

or

sudo /etc/init.d/spawn-fcgi start

You need to make sure that it auto starts on boot, to find that you can easily google how to make a service start on boot, it's very simple