ログを見ると以下のようなエラーが返ってきてました。

502 Bad Gateway Error Nginx connect() to unix:/tmp/unicorn.sock failed

環境

Ruby on Rails4.2.x
unicorn
nginx

解決

*.confファイルのunicorn.sockのパスの位置を確認しましょう。

upstream unicorn_server {
  server unix:/var/www/#{application}/current/tmp/unicorn.sock
  fail_timeout=0;
}

server {
  listen 80;
  server_name sever_name;

  keepalive_timeout 5;

  root /var/www/#{application}/current/public;
  access_log /var/log/nginx/#{application}_access.log;
  error_log /var/log/nginx/#{application}_error.log;

  error_page 500 502 503 504 /500.html;

  try_files $uri/index.html $uri @unicorn;

  location @unicorn {
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Host $http_host;
    proxy_pass http://unicorn_server;
  }

 # location ~ ^/assets/ {
 #   root /var/www/#{application}/current/public;
 # }

  error_page 500 502 503 504 /500.html;
  location = /500.html {
    root /var/www/#{application}/current/public;
  }
}