15-day System Design plan

One focused block per day (about 2–3 hours). Tick days as you go.

Day 1: Estimation & fundamentals

Requirements: functional vs non-functional
Back-of-envelope: QPS, storage, bandwidth
Latency numbers, availability nines

Day 2: Networking & APIs

HTTP/1.1 vs 2 vs 3, TLS, DNS
REST vs gRPC vs GraphQL, idempotency, pagination, versioning

Day 3: Databases I: SQL

Indexes (B-tree), query plans
Normalization, transactions, isolation levels

Day 4: Databases II: NoSQL & storage

Key-value, document, wide-column, graph
CAP, PACELC, consistency models

Day 5: Caching

Cache-aside, write-through, write-back
Invalidation, stampede, hot keys, Redis, CDN

Day 6: Scaling & load balancing

Vertical vs horizontal, L4 vs L7 LB
Sharding, consistent hashing, replication

Day 7: Messaging & async

Kafka vs RabbitMQ vs SQS
Delivery semantics, outbox, idempotent consumers, DLQ

Day 8: Microservices & resilience

Service discovery, API gateway
Circuit breaker, retries, bulkhead, sagas

Day 9: Distributed systems theory

Consensus (Raft/Paxos), leader election
Clocks, ordering, distributed locks, 2PC vs saga

Day 10: LLD I: principles

SOLID, patterns used in LLD
Parking lot, elevator, vending machine

Day 11: LLD II: practice

Rate limiter, LRU cache, logger framework
BookMyShow / splitwise class design

Day 12: HLD I

URL shortener, pastebin, rate limiter service
Notification system

Day 13: HLD II

News feed / Twitter, chat (WhatsApp)
File storage (Dropbox/Drive)

Day 14: HLD III

Uber / ride matching, payment system
Search autocomplete, video streaming

Day 15: Mock interviews & review

2 timed mocks (45 min each)
Review trade-offs, observability, security, failure modes

Pair with the System Design track questions each day.