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ACore Concepts14

A1Client–server model & the request lifecycle
A2Latency, throughput & the numbers every engineer should know
A3Networking: DNS, HTTP/HTTPS, TCP/UDP, TLS
A4API styles: REST, RPC/gRPC, GraphQL — when to use which
A5Data modeling: SQL vs NoSQL, schema design, normalization
A6Indexing & query performance
A7ACID, transactions & isolation levels
A8Caching: strategies, eviction, invalidation
A9Load balancing: L4/L7, algorithms, health checks
A10Replication: leader/follower, multi-leader, leaderless
A11Partitioning, sharding & consistent hashing
A12CAP, PACELC & consistency models
A13Consensus: quorums, Raft/Paxos (conceptual)
A14Back-of-the-envelope estimation

BKey Technologies9

B1Relational workhorses: PostgreSQL / MySQL
B2Wide-column & KV at scale: Cassandra, DynamoDB
B3Redis: cache, data structures, and beyond
B4Search: Elasticsearch & the inverted index

CCommon Patterns11

C1Monolith → microservices; API gateway & service mesh
C2Event-driven architecture & fan-out
C3Idempotency & exactly-once semantics
C4Sagas, 2PC & distributed transactions

DThe Delivery Method5

D1Requirements: functional vs non-functional
D2The Delivery Framework: a timed 5-step walkthrough
D3High-level design & the API-first sketch
D4Deep dives & defending tradeoffs

ELeadership Altitude6

E1Tradeoff frameworks & decision records (ADRs)
E2Platform thinking & build-vs-buy
E3Cost modeling & FinOps
E4Migration & modernization at scale

Practice bank24

T1Foundations5

Design a URL shortener (TinyURL)30 min
Design a pastebin25 min
Design a rate limiter30 min

T2 · MID45 min · Practice Bank

Design a news feed (Twitter / Instagram)

#fanout #caching #sharding #redis

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PREVIOUS · T1 · JUNIORDesign a parking-lot ticketing system

B5Streams & queues: Kafka, SQS, pub/sub

B6Object storage & CDNs: S3, CloudFront

B7Coordination services: ZooKeeper / etcd

B8Stream processing: Flink / Spark

B9Specialty stores: time-series, vector, geospatial

C5CQRS & event sourcing

C6Rate limiting & throttling

C7Backpressure & flow control

C8Distributed locks & leader election

C9Observability: metrics, logs, traces

C10Deploy strategies: canary, blue-green

C11Security: authN/authZ, encryption, DDoS defense

D5Communicating & critiquing a design

E5

SLOs, error budgets & the reliability org

E6Cross-team contracts & API governance

Design an in-memory key-value store35 min

Design a parking-lot ticketing system25 min

T2Common5

Design a news feed (Twitter / Instagram)45 min
Design a chat service (WhatsApp)45 min
Design a notification system40 min
Design a web crawler40 min
Design a link-preview & image service35 min

T3Advanced7

Design a ride-hailing system (Uber)55 min
Design video streaming (YouTube / Netflix)55 min
Design search autocomplete / typeahead45 min
Design a distributed cache50 min
Design a payment system55 min
Design Google Drive / Dropbox50 min
Design a ticket-booking system (Ticketmaster)50 min

T4Expert7

Design a multi-region active-active system60 min
Design a distributed job scheduler55 min
Design a real-time analytics pipeline60 min
Design an ad-serving / bidding platform60 min
Design a globally distributed database60 min
Design a platform-scale distributed rate limiter55 min
Critique: find the failure modes in a given design45 min

NEXT · T2 · MIDDesign a chat service (WhatsApp)

Design a news feed (Twitter / Instagram) — System Design