HLD

Keeping distributed data consistent and services coordinated, then whole designs: notifications, Instagram, Twitter and Uber. 3 modules, about 3 hours of reading. Every lesson ends in something to do.

Consistency and Coordination

Consistency PatternsThe spectrum between strong and eventual, the session guarantees that matter most, and quorum arithmetic.Intermediate17 min
Heartbeats & ChecksumsDetecting dead nodes when you cannot tell slow from dead, and detecting corruption that fails silently.Intermediate18 min
Distributed CoordinationConsensus, leader election, distributed locks and why fencing tokens are the part everyone forgets.Advanced18 min
Gossip Protocol (Epidemic Protocol)Spreading state by telling one random peer at a time — why it converges so fast, how failure is detected, and what it costs.Advanced17 min

Services and Transactions

IdempotencyMaking a retry safe when a timeout leaves you unsure — idempotency keys, the race a naive implementation misses, and storing responses.Intermediate18 min
Distributed Transactions (SAGA Pattern)Losing atomicity across services — sagas and compensation, choreography versus orchestration, and why two-phase commit faded.Advanced17 min
Microservices ArchitectureWhat splitting a monolith actually costs, where the boundaries go, and why the distributed monolith is the worst outcome.Advanced20 min

Case Studies

Notification SystemsFan-out across push, email and SMS, third-party failure, deduplication and not annoying your users.Intermediate17 min
Design InstagramA full worked case study — requirements, estimates, media pipeline, feed generation and the trade-offs at each step.Advanced21 min
Design TwitterTimelines at scale, the celebrity hot-key problem in full, trending topics and real-time delivery.Advanced18 min
Design UberWrite-heavy location tracking, geospatial indexing with geohash and quadtrees, and matching without double-booking.Advanced19 min

Consistency and Coordination

Services and Transactions

Case Studies

Consistency and Coordination

Services and Transactions

Case Studies

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