System Design Concepts

TCP/UDP, DNS, HTTP, reverse proxy, load balancing, CDN, WebSockets, and API protocols

Indexes, RDBMS internals, SQL vs NoSQL, Redis, Cassandra, S3, caching, and full-text search

Database sharding — hash, range, directory strategies and cross-shard operations

Leader-based replication, read replicas, replication lag, and consistency models

CAP, PACELC, consistency models, idempotency, distributed locking, leader election, gossip, and quorum

Two-Phase Commit, Raft consensus, log replication, and safety guarantees

Message queues vs event streams, RabbitMQ, SQS, Kafka, consumer groups, and hybrid patterns

Fixed window, sliding window, token bucket, leaky bucket, distributed implementations, and Redis Lua scripts

Circuit breaker, bulkhead isolation, back-pressure, load shedding, and composing resilience patterns

Pagination strategies, idempotency keys, API versioning, breaking vs non-breaking changes, and sunset lifecycle

Microservices vs monolith, service discovery, API gateway, BFF pattern, and service mesh

Latency numbers, estimation framework, worked examples, peak load patterns, and interview worksheet

Typeahead autocomplete, GeoHash encoding, QuadTree spatial indexing, and Uber-style location indexing

OAuth 2.0, OIDC, JWT structure and validation, API authentication patterns — API keys, HMAC, mTLS, and Bearer tokens

Batch vs streaming, stream processing engines, data warehouses, and Change Data Capture with Debezium

Recommendation systems (retrieval + ranking), feature stores with point-in-time correctness, and end-to-end ML platforms