Its built with Flask and uses the Rackspace Cloud Files object store for...storage...of...objects. Tiny tiny objects.
It works by turning a loooong url into a short code (through magic!). The short code is then uploaded as an object to Cloud Files, and served up via the Cloud Files CDN service. This allows you to expand url's without having to go through the blk.io web service again, and will work as long as the CDN and CloudFiles is online (which better be always).
The contents of the uploaded object is just a simple HTML page that redirects a visitor the original long url when its accessed via CDN at http://small.blk.io/[SomeShortCode]:
fhines@kira:~$ http http://small.blk.io/e08e9d HTTP/1.1 200 OK Accept-Ranges: bytes Cache-Control: public, max-age=259160 Connection: keep-alive Content-Encoding: gzip Content-Length: 274 Content-Type: text/html Date: Mon, 07 Oct 2013 07:10:56 GMT ETag: b592164ee9183282f9b2259d154d23cf Expires: Thu, 10 Oct 2013 07:10:16 GMT Last-Modified: Mon, 07 Oct 2013 06:41:14 GMT Vary: Accept-Encoding X-Object-Meta-Longurl: http://bloomberg.com X-Timestamp: 1381128074.94653 X-Trans-Id: txb4163f76b17c4753bc188-0052525e7fdfw1 <!DOCTYPE HTML> <html lang="en-US"> <head> <meta charset="UTF-8"> <meta http-equiv="refresh" content="1; url=http://bloomberg.com"> <script> window.location.href = "http://bloomberg.com" </script> <title>http://bloomberg.com - Page Redirection</title> </head> <body> If you are not redirected automatically to <a href='http://bloomberg.com'>http://bloomberg.com</a> follow <a href='http://bloomberg.com'>this link</a> </body> </html>
In addition, when the object is stored in Cloud Files a meta data key called "X-Object-Meta-Longurl" is also set pointing to the original url. This allows you to determine the long url of a shortcode stored in Cloud Files by simply performing a head on the object. This is the method used by the Flask app when expanding a url by hitting http://blk.io/[SomeShortCode]
Other handy things you could do ? Use Cloud Files expiring object support to automatically expire url's...and other stuff, and things, yea...