Nginx proxy_pass to variable with trailing slash fails

Question

I'm having an issue where I need to make the proxy_pass a variable, but when I make it a variable, it fails to resolve correctly on the backend server

nginx -v
nginx version: nginx/1.6.2

This is the working one:

  server {
    listen 443 ssl;
    ssl on;
    server_name api.hostname.com;

    include ssl_params;

    location = /v1 {
      return 302 /v1/;
    }

    location /v1/ {
      proxy_pass        http://internal-api.hostname.com.us-east-1.elb.amazonaws.com/;
      proxy_set_header  Host            $host;
      proxy_set_header        X-Real-IP       $remote_addr;
      proxy_set_header  X-Forwarded-For $proxy_add_x_forwarded_for;
    }

  }

This is a broken one

  server {
    listen 443 ssl;
    ssl on;
    server_name api.hostname.com;

    include ssl_params;

    location = /v1 {
      return 302 /v1/;
    }

    location /v1/ {
      resolver 10.0.0.2;
      set $backend "http://internal-api.hostname.com.us-east-1.elb.amazonaws.com/";
      proxy_pass        $backend;
      proxy_set_header  Host            $host;
      proxy_set_header        X-Real-IP       $remote_addr;
      proxy_set_header  X-Forwarded-For $proxy_add_x_forwarded_for;
    }

  }

The backend results for https://api.hostname.com/v1/profile on the working one is:

<-- GET /profile
--> GET /profile 200 16ms 349b

But on the broken one

<-- GET /
--> GET / 401 1ms 12b

I've tried with:

set $backend "internal-api.hostname.com.us-east-1.elb.amazonaws.com";
proxy_pass http://$backend/

set $backend "internal-api.hostname.com.us-east-1.elb.amazonaws.com/";
proxy_pass http://$backend/

Any time I'm using variables in the proxy_pass, it forwards everything to / (root) on the backend, definitely not what I was intending.

Answer 1

I have exactly the same problem (need variable because on AWS the internal IP change). After two days of test/investigation, I think have found a working configuration (with no / in variable or proxy_pass but with a "rewrite break" for remove the unwanted path on backend request):

resolver 10.0.0.2;
set $backend "http://internal-api.hostname.com.us-east-1.elb.amazonaws.com";
location /v1/ {
      proxy_pass        $backend;
      proxy_set_header  Host            $host;
      proxy_set_header        X-Real-IP       $remote_addr;
      proxy_set_header  X-Forwarded-For $proxy_add_x_forwarded_for;
      rewrite ^/v1/(.*) /$1 break;
}

Answer 2

Use the upstream module to set the variable:

http {

    ...

    upstream backend {
        server internal-api.hostname.com.us-east-1.elb.amazonaws.com;
    }

    ...

    server {

        ...

        location /v1/ {
            proxy_pass http://backend;

            ...

        }
    }
}

The upstream module is a standard module and would have had to have been specifically disabled for it not to be in your installation of Nginx.