These concepts should be automatic:
Scaling: Vertical vs horizontal. Stateless services. Load balancing algorithms.
Databases: SQL vs NoSQL trade-offs. ACID vs BASE. Indexing. Replication. Sharding.
Caching: Cache-aside, write-through, write-behind. Eviction policies. Cache invalidation.
Async processing: Message queues. Pub/sub. Delivery guarantees.
Storage: Block vs object vs file. CDNs. Data lakes vs warehouses.
If any of these feel shaky, review our System Design Interview Prep roadmap sections -.