The classic pressure test
Interviewers often ask what happens if traffic grows ten or a hundred times. This tests whether your design has headroom and whether you know which part breaks first. A calm, structured answer shows you understand your own system.
Where systems break
- A single database that cannot hold the writes.
- A hot key or partition that one shard cannot serve.
- A stateful service that cannot simply be cloned.
- A cache too small to keep the working set hot.
The scaling toolbox
- Replicate reads to spread read load.
- Shard writes to spread write load by key.
- Scale stateless services horizontally behind a balancer.
- Add queues to absorb bursts and smooth load.
Answer in order
Name the part that breaks first, apply the fitting technique, then find the next bottleneck the fix exposes. Scaling is iterative, and showing that loop is the point of the question.
Key idea
When asked to grow traffic by orders of magnitude, find the first bottleneck, apply replication or sharding, then move to the next one the fix reveals.