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Every HTTPS request starts with a handshake. Terminating TLS for millions of connections - and issuing, rotating, and revoking the certificates behind it - is a system-design problem in its own right.
Design the TLS layer for a large web platform or CDN: terminate HTTPS for millions of concurrent connections across many domains, and manage the full certificate lifecycle - issuance, renewal, rotation, and revocation - with no downtime and no expired-cert incidents.
This is a Hard topic because TLS sits on the hot path of 100% of traffic, the handshake is CPU-expensive, and the failure modes are brutal: an expired certificate is an instant, total, user-visible outage (the single most common "the whole site is down" incident). It tests whether you understand the protocol's cost model and the operational machinery that keeps certificates valid.
Asking these before diving into a solution is the difference between a "hire" and a "no signal" rating. Pick the questions whose answers would change your design.
Capacity estimation · architecture with all 6 components explained · 4 deep dives · trade-off analysis · 8 common follow-up questions
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Edge cache hierarchies, cache key design, invalidation, origin shield, and edge compute - the system every other system relies on without thinking about it.
L4 vs L7, consistent hashing, health checks, connection draining, and the difference between a fleet that survives partial failures and one that cascades into outage.
The front door to a microservice fleet. One layer that every external request crosses - so it owns auth, rate limiting, routing, and resilience, and absolutely cannot become the bottleneck.
The internet's phone book. A globally distributed, read-dominated, cache-everywhere hierarchy that has to answer in single-digit milliseconds and never go down.
Reading is the floor. The interview signal is in walking through this live with someone probing follow-ups. Use the AI mock interview to practice talking through requirements, architecture, and trade-offs out loud.
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