TIL: Fixing HTTP 502 Bad Gateway error (nginx & WordPress)

My wife has a WordPress blog hosted on my server. Few days ago, MySQL server went down for some reasons (just like that) and of course her blog was broken. I was trying to recover but had no luck. So I reinstalled MySQL server on the server and setup the blog with a backup DB. The blog is working now.

Then I found out that I couldn’t change permalink format to “pretty URLs” because rewrite rules were not set up properly. With my very little knowledge on configuring virtual host nginx, in the end I got 502 — Bad Gateway error on the blog.

I wasn’t surprised at all though …

Basically I put wrong virtual host configurations to the config file. I was googling and found this article very helpful:

Fix "502 Bad Gateway" error on NGINX server after upgrading PHP * JvdC.me

However it didn’t solve the problem until I came across another blog post:

Solving "502 Bad Gateway" with nginx & php-fpm | Wildly Inaccurate

And it turned out that all I had to do is changing the value of fastcgi_pass from a Unix socket value to an IP address + port like mentioned in the post, even though the .sock file exists on the server.

To summarize, here is how I fix the 502 error:

• In the file /etc/php/7.0/fpm/pool.d/www.conf , change listen = /run/php/php7.0-fpm.sock to listen = 127.0.0.1:9000
• Set Virtual Host config file like this

upstream php {
  server unix:/tmp/php-cgi.socket;
  server 127.0.0.1:9000;
}
server {
  listen 80;
  root /var/www/html/nemo.in.th;
  index index.php index.html index.nginx-debian.html;
  server_name nemo.in.th;
  
  location / {
    try_files $uri $uri/ /index.php?$args;
  }
 
  location ~ \.php$ {
    #NOTE: You should have “cgi.fix_pathinfo = 0;” in php.ini
    include fastcgi.conf;
    include fastcgi_params;
    fastcgi_pass php;
  }
}

My wife’s blog is back to life again.