Scalability and High Availability are most decisive
Besides a solid network infrastructure, the system concept is most important:
- server redundancy: all important tasks run on multiple servers (e.g. loadbalancers, databases, backend and frontend servers)
- component redundancy: multiple power supplies and RAID concepts per server
- multiple power supply circuits
- high level of security of easy to administer linux boxes
- avoidance of any kind of "Single-Point-of-Failures"
- external CDN (content delivery network) for failover, loadbalancing or geographic delivery
- capacity bottlenecks can easily bypassed through adding any amount of virtual server instances
- cloud computing connection




