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System Design Lessons

Every lesson in the System design course, free to read. Each skill has a lesson that starts simple and gets technical, and a quick revise page. Practice and progress tracking need a free account.

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System Design Fundamentals

How a system design interview runs, how to size a system with back-of-the-envelope numbers, and a first complete design - scaling a read-heavy service.

Building Blocks

The components every design is assembled from - load balancers, caches, replicated and partitioned databases, message queues - and the consistency trade-offs that come with spreading data across machines.

Load Balancing and API Gateways

Load Balancers, Gateways and Rate LimitsHow traffic reaches healthy servers: balancing algorithms, health checks, L4 versus L7, sticky sessions, API gateways and edge rate limiting.

Caching

Caching StrategiesWhere a cache sits and how it stays correct: read and write patterns, eviction, TTLs and invalidation, hot keys and stampedes, and CDNs.

Databases and Replication

Replication and Choosing a Data StoreSQL or NoSQL for a workload, leader-follower replication, synchronous versus asynchronous, replication lag and read-your-writes, and failover.

Partitioning and Consistent Hashing

Sharding and Consistent HashingPicking a shard key for the hot query, hash versus range partitioning, consistent hashing, hot partitions and queries that span shards.

Message Queues and Async Processing

Queues and Asynchronous ProcessingQueues versus logs, at-least-once delivery and idempotent consumers, ordering by key, back-pressure, retries and dead-letter queues.

Consistency and Availability

CAP, Consistency Models and QuorumsWhat a network partition forces you to choose, strong versus eventual consistency, quorum reads and writes, and PACELC's latency trade-off.

Design Problems

Complete designs of well-known systems on the design canvas - a news feed, a chat service and a video platform - each checked against its requirements and failure modes.

News Feed

Design a News FeedPosting and reading a personalized feed at scale: fan-out on write or read, the celebrity problem, timeline caches and media storage.

Chat System

Design a Chat SystemReal-time messaging: WebSocket gateways, routing between servers, message storage and ordering, delivery receipts, presence and offline push.

Video Streaming

Design a Video Streaming ServiceFrom upload to playback: resumable uploads to object storage, a transcoding pipeline, adaptive bitrate streaming and global delivery through a CDN.

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