- This is a very interesting overview (basically a summary) of YouTube's architecture and how it handles scalability. Python is used all over the place. Includes lessons learned! Of course YouTube does not need heavy business-logic nor a solid transaction-architecture as mentioned here too. This makes scaling a little less of a challenge; but since the numbers are so huge, the challenges are nevertheless large.
This (a bit older) article describes how Digg handles scalability. Definitely interesting too.
And here's the inside scoop on MySpace architecture and scalability.
Here are details on Google's file system GFS and how it helps solve them scalability.
This PDF shows how Japan's largest social networking site (SNS) Mixi is handling scalability with MySQL.
Finally, interesting regarding scalability and availability is this architecture "mashup": Java JVM is used to improve scalability in Drupal.
- This looks like an interesting upcoming feature in HTMLUnit for unittesting AJAX enabled web-applications. It will actually re-synchronize AJAX calls that should run asynchronously.