More Goals...

Speed
Yahoo MUST be fast
Yahoo MUST be first (CTO story)
Redundancy
No single points of failure
No single points of congestion
Flexibility
Our architectural needs change often
New products are invented in weeks
Change is the only constant at Yahoo
Fault Tolerance
In a big network, things die.
They do so ALL THE TIME
Graceful Failures
Things shouldn't blow up, if possible
But we do need to know if they try to