How does Stack Overflow scale without any failures? What is its hardware configuration?
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For the Hardware / Sysadmin perspective you can find a lot of information about how things have been built out at http://blog.serverfault.com .
My biggest personal advice with scaling is that it is a cross-functional team based effort. For example, a lot of scaling is having good code, but you want also want good hardware and proper configurations, and a sound network architecture.