Nginx dynamic proxy_pass doesn't resolve properly

Solution 1:

When you are using variables in a proxy_pass directive, nginx will use runtime resolving except if :

• the target server is declared as an IP address
• the target server name is part of an upstream server group
• the target server name has already been resolved (e.g. it matches a server name in another server block)

Here, a runtime resolver won't help as localhost may not be resolved by a DNS. Also it's a waste to have runtime resolving as you can clearly avoid it here.

So, two simple solutions :

• use 127.0.0.1
• declare an upstream block if you have server names or a pool of target servers

Now you need your proxied server redirection to be correct. So either :

• your proxy target handles the host header and you pass it through with :

  proxy_set_header "Host" $host;

• your proxy target can't handle the Host header for redirects and you need to rewrite them with nginx using :

  proxy_redirect http://$proxy_host/$sub_domain http://$host;

However if it doesn't support the Host header at all, links will be broken.