System Design

Understand the difference between horizontal (scale-out) and vertical (scale-up) scaling, their trade-offs, and when to use each approach.

Run Redis as a cache: data structures, TTLs and eviction, persistence trade-offs, replication, clustering, hot keys, and stampede protection.

Master database sharding strategies: horizontal partitioning, shard key selection, cross-shard queries, rebalancing, and handling failures in sharded systems.

Learn consistent hashing for distributed systems. Understand how it enables efficient data distribution, handles node failures, and minimizes data movement duri

Master replication models (primary-replica, multi-primary), sync vs async trade-offs, replication lag, read consistency, and failover.

Learn database indexing strategies: B-tree, hash indexes, composite indexes, covering indexes, and how to design indexes for optimal query performance.

When one app is enough—and when splitting into services actually helps. Plain comparison of monoliths and microservices, how teams feel the difference in production, and how to migrate without a big-bang rewrite.

Master microservices architecture: service decomposition, communication patterns, data management, deployment strategies, and challenges like distributed transa

Understand API gateways as the single entry point for microservices. Learn routing, authentication, rate limiting, request/response transformation, and circuit

Master event-driven architecture: event sourcing, CQRS, event streaming, event choreography vs orchestration, and building scalable event-driven systems.

Design safe retries: exponential backoff + jitter, timeouts, idempotency, circuit breaking, and avoiding retry storms.

Why teams use rate limits, real-world examples, how one request is checked at the gateway, the per-server mistake, and rate limiting vs throttling—in plain English.

Compare fixed window, token bucket, leaky bucket, and sliding window rate limiting—and what API clients should see when blocked (429, headers, Retry-After).

Understand Content Delivery Networks (CDNs), how they reduce latency, edge caching strategies, cache invalidation, and designing a CDN architecture.

Understand reverse proxies (Nginx/Envoy): TLS termination, routing, load balancing, caching, auth, and common deployment patterns.

Design for high availability: redundancy, failover strategies, health checks, circuit breakers, and achieving 99.9%+ uptime in distributed systems.

Master CQRS (Command Query Responsibility Segregation): separate read and write models, when to use it, and implementation patterns.

Learn event sourcing: storing state changes as events, rebuilding state, event replay, and when event sourcing is the right choice.

Learn sagas for distributed transactions: choreography vs orchestration, compensations, idempotency, and failure handling.