Designing a Scalable Twitter

There were many talks recently about twitter scalability and their specific choice of language such as Scala to address their existing Ruby based scalability. In this post i tried to provide a more methodical approach for handling twitter scalability challenges that is centered around the right choice of architecture patterns rather then the language itself.
The architecture pattern are given in a generic fashion that is not specific to twitter itself and can serve anyone who is looking to build a scalable real time web application in the near future.