nginxを使ったreproxyの最小（に近い）設定

nginx.conf

worker_processes  1;

error_log  logs/error.log;

daemon off;

events {
    worker_connections  1024;
}

http {
    include       mime.types;
    default_type  application/octet-stream;

    server {
        listen       8081;
        server_name  localhost;

        location / {
            proxy_redirect          off;
            proxy_set_header        Host            $host;
            proxy_pass   http://127.0.0.1:4567;
        }

        location /reploxy {
            internal;
            resolver 8.8.8.8;
            set $reproxy  $upstream_http_x_reproxy_url;
            proxy_pass $reproxy;
        }

        error_page   500 502 503 504  /50x.html;
        location = /50x.html {
            root   html;
        }

    }

}

test.rb

require 'sinatra'

get '/' do
  response['X-Accel-Redirect'] = '/reploxy'
  response['X-Reproxy-URL'] = 'http://www.sinatrarb.com/images/logo.gif'
end