Ask HN: building your own CDN - how to do it?

Let's say that you can't use AWS or other cloud-based systems out there and that you need to roll your own CDN. You need to:

1) Have multiple cloned servers in 3-5 locations

2) Have a way to route a specific customer's address to the location nearest them.

My thinking is to use a managed DNS service like UltraDNS or Route 53. Any other thoughts?

Thanks -