Why 502 error when installing php5-fpm + nginx?

Question

PHP

I am learning to configure the server manually on VDS. Installed nginx + php5-fpm. I don’t understand why it is necessary to specify 127.0.0.1, and not the address of my server. Although I put the address, nothing happened.
But I can't set it up correctly. Here is the server itself, nginx is running, but the 502 error is 176.112.212.179/index.php

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

        root /var/www/htdocs;
        index index.php;

        location / {
           try_files $uri $uri/ =404;
        }

location ~ \.php$ {
        # fastcgi_split_path_info ^(.+\.php)(.*)$;
        fastcgi_pass   127.0.0.1:9000;
        fastcgi_index  index.php;

        fastcgi_param  DOCUMENT_ROOT    /htdocs;
        fastcgi_param  SCRIPT_FILENAME  /htdocs$fastcgi_script_name;
        fastcgi_param  PATH_TRANSLATED  /htdocs$fastcgi_script_name;

        include fastcgi_params;
        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_intercept_errors        on;
        fastcgi_ignore_client_abort     off;
        fastcgi_connect_timeout 60;
        fastcgi_send_timeout 180;
        fastcgi_read_timeout 180;
        fastcgi_buffer_size 128k;
        fastcgi_buffers 4 256k;
        fastcgi_busy_buffers_size 256k;
        fastcgi_temp_file_write_size 256k;
    }

        location ~* ^.+.(js|css|png|jpg|jpeg|gif|ico)$ {
            access_log        off;
            expires           max;
        }

        location ~ /\.ht {
            deny  all;
    }

}

What is the problem?

Answer 1

php-fpm usually listens on 127.0.0.1 port 9000, which is what you specify as the backend.
This is done so that it is impossible to access your server as server.ru:9000 and get directly to php-fpm.
For any misunderstandings - see the logs - /var/log/ nginx and php-fpm logs