title: ngnix - duplicate upstream "app_server" in /etc/nginx/sites-enabled/django
body: <p>Accidentally deleted conf nginx filled<code>/etc/nginx/sites-enabled/django
  </code> , then filled it with the same configuration settings. got the following error:</p>
  
  <pre><code>  Feb 02 12:56:53 solomon nginx[32004]: nginx: [emerg] duplicate upstream "app_server" in /etc/nginx/sites-enabled/django.save:1
  Feb 02 12:56:53 solomon nginx[32004]: nginx: configuration file /etc/nginx/nginx.conf test failed
  Feb 02 12:56:53 solomon systemd[1]: nginx.service: Control process exited, code=exited status=1
  Feb 02 12:56:53 solomon sudo[31990]: pam_unix(sudo:session): session closed for user root
  Feb 02 12:56:53 solomon systemd[1]: Failed to start A high performance web server and a reverse proxy server.
  -- Subject: Unit nginx.service has failed
  -- Defined-By: systemd
  -- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
  -- 
  -- Unit nginx.service has failed.
  -- 
  -- The result is failed.
  Feb 02 12:56:53 solomon systemd[1]: nginx.service: Unit entered failed state.
  Feb 02 12:56:53 solomon systemd[1]: nginx.service: Failed with result 'exit-code'.
  </code></pre>
  
  <p>Configuration, which worked before for sure. Have I done something incorrectly ?:</p>
  
  <pre><code> upstream app_server {
      server 127.0.0.1:9000 fail_timeout=0;
  }
  
  server {
      listen 80 default_server;
      listen [::]:80 default_server ipv6only=on;
  
      root /usr/share/nginx/html;
      index index.html index.htm;
  
      client_max_body_size 4G;
      server_name _;
  
      keepalive_timeout 5;
  
      # Your Django project's media files - amend as required
      location /media  {
          alias /home/django/django_project/django_project/media;
      }
  
      # your Django project's static files - amend as required
      location /static {
          alias /home/django/django_project/django_project/static; 
      }
  
      location / {
          proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
          proxy_set_header Host $http_host;
          proxy_redirect off;
          proxy_pass http://app_server;
      }
  }
  </code></pre>