Proxy to "backend" service whenever a file does not exists

Question

I'm using NGINX to serve static file.

Whenever a file does not exist, I want NGINX to hit a nodejs backend service that will try to asynchronously retrieve that file.

The backend service needs 3 arguments: the GUID, the size and the extension of the file. All these arguments are retrieved from the original request using a regex.

Here is my current NGINX configuration file:

server {
  listen 80;
  server_name .example.com;
  root /var/www;

  ## Serves file (matching pattern: /<size>/<MEDIA>/<file na-me><.ext>)
  location / {
    location ~* ^/(\d+x\d+)/(([\w])([\w])([\w])[-\w]+)/[^\.]+\.(\w+)$ {
      try_files /$3/$4/$5/$2/$1.$6 @backend/$2/$1/$6;
    }
  }

  ## backend service
  location @backend {
    proxy_pass http://127.0.0.1:8080;
  }
}

But I keep getting this error:

2012/01/23 11:53:31 [error] 28354#0: *1 could not find named location "@backend/ed3269d1-f9ef-4Ffc-dbea-5982969846c0/200x240/jpg", client: XXX.XXX.XXX.XXX, server: example.com, request: "GET /200x240/ed3269d1-f9ef-4Ffc-dbea-5982969846c0/my%20fil.jpg HTTP/1.1", host: "3.example.com"

Any idea how I can get NGINX to "proxy" the request to the backend service instead of looking for a file?

I got it working by removing the "/$2/$1/$6" part after "@backend" in the **try_files** directive. But I still need these arguments. — ZogStriP, Jan 23 '12 at 17:03

score 2 · Accepted Answer · answered Jan 23 '12 at 18:17

If you use named captures for the captures, you can use them to rewrite the request in your named location:

server {
  listen 80;
  server_name .example.com;
  root /var/www;

  ## Serves file (matching pattern: /<size>/<MEDIA>/<file na-me><.ext>)
  location / {
    ## ?<name> assigns the capture to variable $name
    location ~* ^/(?<size>\d+x\d+)/(?<guid>([\w])([\w])([\w])[-\w]+)/[^\.]+\.(?<ext>\w+)$ {
      try_files /$3/$4/$5/$2/$1.$6 @backend;
    }
  }

  ## backend service
  location @backend {
    ## rewrite ... break; just sets $uri and doesn't perform a redirect.
    rewrite ^ /$guid/$size/$ext break;
    proxy_pass http://127.0.0.1:8080;
  }
}

Proxy to "backend" service whenever a file does not exists

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