nginx – Configuring NGINX as a Mail Proxy Server with Load Balancing Based on User

You should be able to add something like this in front of the other location block:

location /upload {
  break;
}

location /admin {
  break;
}

if ($request_method = POST ) {
  break;
}

Update:

nginx first searches for the most specific location given by literal strings regardless of the listed order. In the configuration above the only literal location is “/” and since it matches any request it will be used as a last resort. Then nginx checks locations given by regular expression in the order listed in the configuration file. The first matching expression stops the search and nginx will use this location. If no regular expression matches a request, then nginx uses the most specific literal location found earlier.

So, the /upload and /admin location blocks are literals and are processed after the regex you're using for the proxy.

Try "location ~ ^/admin" and so on.

What you want is an active+passive setup. Here's an example nginx conf snippet to get you going:

upstream backend {
    server 1.2.3.4:80 fail_timeout=5s max_fails=3;
    server 4.5.6.7:80 backup;
}

server {
    listen 80;
    server_name whatevs.com;

    location / {
        proxy_pass http://backend;
    }
}

So, 'normally', all requests will go to host 1.2.3.4. If we get three failures to that box, then 4.5.6.7 will take over.