System Design Advanced · Week 6

Real-time at scale: WebSocket fan-out, presence, rooms

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System Design Advanced • Week 6

01 / 13

Real-time at scale: WebSocket fan-out, presence, rooms

Token bucket = refill steadily, burst up to capacity, then wait.

StackShade deck

Predict → explain → retrieve

COURSE CONTENTS

Real-time at scale: WebSocket fan-out, presence, rooms

01Consistent Hashing & Data PartitioningWeek 1 · 5 topics0/5

Sharding & the modulo-N trap (visual deep dive)12 min Consistent hashing ring simulator15 min Virtual nodes and balanced load12 min Dynamo-style partitioning in the wild (Cassandra, Memcached)14 min Compute key movement when a 5th node joins (by hand)20 min

02Distributed Caching at ScaleWeek 2 · 5 topics0/5

Cache-aside vs write-behind (with the stampede bug)12 min Reproduce + fix a cache stampede in the simulator12 min Hot keys, key skew and celebrity mitigation12 min Memcached vs Redis architectures; cache clusters14 min Design the cache layer for a viral-tweet scenario30 min

03Event-Driven Architecture & Message QueuesWeek 3 · 5 topics0/5

Delivery guarantees & idempotent consumers14 min Kafka internals: partitions, offsets, consumer groups16 min Ordering, retries, dead-letter queues12 min Interactive: partition assignment across a consumer group12 min Design an event pipeline for order processing40 min

04Consensus, Replication & Leader ElectionWeek 4 · 5 topics0/5

Distributed consensus & the replication log12 min Raft walkthrough: terms, votes, log matching16 min Split-brain and why quorum saves you12 min Paxos vs Raft vs gossip — picking a coordination style12 min Simulate: 5-node cluster survives 2 failures?25 min

05Distributed TransactionsWeek 5 · 4 topics0/4

2PC and why it blocks (and where it's still used)14 min Sagas: choreography vs orchestration14 min Outbox pattern: events that never lie about the DB12 min Design payment flow with saga compensations35 min

06Rate Limiting, Gates & Real-TimeWeek 6 · 5 topics0/5

Token bucket, leaky bucket, sliding window14 min Interactive: rate limiter algorithms visualizer12 min API gateways: auth, quotas, routing in one hop12 min Real-time at scale: WebSocket fan-out, presence, rooms14 min Design rate limiting for a public API (per-user + global)30 min

07Case Studies I: Social & MessagingWeek 7 · 4 topics0/4

Design Twitter: feeds, fan-out, celebrities22 min Design WhatsApp: chats, delivery ticks, groups22 min Design Instagram: media pipeline + feed ranking hooks18 min Solo: design a chat system with read receipts45 min

08Case Studies II: Infra-Scale SystemsWeek 8 · 5 topics0/5

Design Uber: geohashes, matching, surge24 min Design YouTube: upload, transcode, CDN delivery22 min Design Google Drive: sync, chunks, conflicts20 min Design a web crawler + typeahead (bonus)18 min Full mock: 45-min design of your choice + rubric self-review60 min