I have installed Gitlab CE version. I can find nginx bundled in Gitlab. However I cannot find a way to restart nginx separately. I have tried sudo service nginx restart but it gives:
* Restarting nginx nginx                                     [fail] 
I have checked all the document but cannot find a solution. I am trying to add vhost to the bundled nginx according to this tutorial. But I stuck at that step. Is there other way to add vhost to bundled nginx with Gitlab? Or How can I check whether my nginx conf work?
Edit: 502 error I have solved.
I try to use NON-bundle nginx according to this doc , But after I modify gitlab.rb and run sudo gitlab-ctl reconfigure , I got 502 Whoops, GitLab is taking too much time to respond. error. 
Here is my gitlab.conf for nginx.
upstream gitlab {
  server unix://var/opt/gitlab/gitlab-git-http-server/sockets/gitlab.socket fail_timeout=0;
  #
}
server {
  listen *:80;
  server_name blcu.tk;
  server_tokens off;
  root /opt/gitlab/embedded/service/gitlab-rails/public;
  client_max_body_size 250m;
  access_log  /var/log/gitlab/nginx/gitlab_access.log;
  error_log   /var/log/gitlab/nginx/gitlab_error.log;
# Ensure Passenger uses the bundled Ruby version
passenger_ruby /opt/gitlab/embedded/bin/ruby;
# Correct the $PATH variable to included packaged executables
passenger_env_var PATH "/opt/gitlab/bin:/opt/gitlab/embedded/bin:/usr/local/bin:/usr/bin:/bin";
# Make sure Passenger runs as the correct user and group to
# prevent permission issues
passenger_user git;
passenger_group git;
# Enable Passenger & keep at least one instance running at all times
passenger_enabled on;
passenger_min_instances 1;
location / {
  try_files $uri $uri/index.html $uri.html @gitlab;
}
 location @gitlab {
    # If you use https make sure you disable gzip compression 
    # to be safe against BREACH attack
    proxy_read_timeout 300; # Some requests take more than 30 seconds.
    proxy_connect_timeout 300; # Some requests take more than 30 seconds.
    proxy_redirect     off;
    proxy_set_header   X-Forwarded-Proto $scheme;
    proxy_set_header   Host              $http_host;
    proxy_set_header   X-Real-IP         $remote_addr;
    proxy_set_header   X-Forwarded-For   $proxy_add_x_forwarded_for;
    proxy_set_header   X-Frame-Options   SAMEORIGIN;
    proxy_pass http://gitlab;
  }
  location ~ ^/(assets)/  {
    root /opt/gitlab/embedded/service/gitlab-rails/public;
    # gzip_static on; # to serve pre-gzipped version
    expires max;
    add_header Cache-Control public;
  }
  error_page 502 /502.html;
}