Reddit reviews High Performance Drupal: Fast And Scalable Designs

High Performance Drupal was a very good resource for me.

Granted, the book is a little more high performance oriented than high availability, but it does deal with creating a high traffic website specifically for Drupal which requires some redundancy. It will likely give you some valuable insight into how to create your architecture. If nothing else, it may save you from having to throw extra hardware at a performance problem.