At 10× the initial load, the bottleneck is almost always the database. The first evolution is read replicas. At 100× load, the bottleneck moves to the read replicas themselves, requiring sharding. Each evolution step changes the data access patterns and may invalidate caching strategies.
The design process does not change at scale — the same five phases apply. The difference is that scale estimates change which solutions are on the table. What is a single-server solution at 1,000 QPS becomes a distributed system problem at 100,000 QPS.