Using Nginx as a caching proxy for Refile with Ruby on Rails

nginx.conf

http {
    ...
    proxy_cache_path /data/perch.squaremill.com/shared/image_cache levels=1:2 keys_zone=images:10m;
    ...
}

server.conf

server {
   listen 80;
   
   server_name www.somedomain.com;
   
   location /attachments {    
     proxy_pass http://127.0.0.1:81;
     proxy_ignore_headers Set-Cookie;
     proxy_hide_header Set-Cookie;
     proxy_cache images;
   }
  
   location / {
     proxy_set_header X-Real-IP $remote_addr;
     proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
     proxy_set_header Host "www.somedomain.com:80";
     proxy_redirect off;
     proxy_pass http://127.0.0.1:81/;
   }
} 

server {
    listen 81;
    server_name somedomain.com;

    root /data/somedomain.com/current/public;

    passenger_enabled on;
    rack_env production;
    passenger_min_instances 2;

    location ~ ^/assets/ {
      expires 1y;
      add_header Cache-Control public;
      # to serve pre-gzipped version, requires nginx compiled with this
      gzip_static on;

      # Some browsers still send conditional-GET requests if there's a
      # Last-Modified header or an ETag header even if they haven't
      # reached the expiry date sent in the Expires header.
      add_header Last-Modified "";
      add_header ETag "";
      break;
    }
}