System Design Interview Prep

The 45-Minute Interview Framework

0–5 Minutes (Requirements): Split into functional features (limit to top 3) and non-functional requirements (read/write ratio, latency budgets, and consistency).
5–10 Minutes (Estimations): Do quick back-of-the-envelope math for Daily Active Users (DAU), storage, bandwidth, and memory needs.
10–15 Minutes (High-Level Design): Draw end-to-end data flows using basic clients, load balancers, application servers, and databases.
15–40 Minutes (Deep Dive): Focus 80–90% of your score here by addressing bottlenecks, single points of failure, sharding, and caching trade-offs.
40–45 Minutes (Wrap-up): Summarize trade-offs, mention what you would monitor, and discuss how to scale further under 10x load.

Storage & Databases: Relational vs. NoSQL, ACID vs. BASE, replication, and sharding strategies.
Scalability: Horizontal vs. vertical scaling, consistent hashing, and load-balancing algorithms.
Performance & Caching: Redis/Memcached patterns (write-through, cache-aside), CDNs, and latency numbers every engineer should know.
Asynchronous Processing: Message queues (Kafka, RabbitMQ) to decouple heavy or spike-prone workflows.
Reliability: CAP theorem, PACELC theorem, circuit breakers, and rate limiters.