We want the backend architecture to be cheap (requires fewer servers), best performance, fault tolerant, and scalable. I would like to find out if someone has experience in deploying such a solution and may be wants to share their strategy + architecture?

Here are some further details, which I've come up with so far:

system will be deployed on CentOS on Amazon EC2 run multiple versions of NodeJS separate from one another use NginX as load balancer between multiple NodeJS instances (also does gzip compression) MongoDB for storing account information mongoose or NginX for serving static files