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Real-Time App Patterns at Scale
Created by Shaunak Ghosh
Design real-time features that feel instantaneous at scale by connecting UX latency/freshness expectations to transport choices, scalable event fanout, and correctness primitives. You’ll learn when to use polling vs WebSockets vs SSE, how to make retries safe with idempotency and snapshots, how to ship optimistic UI with reliable rollback, and how offline/reconnect and E2EE constraints change your architecture decisions.
Requirements
- Comfort with HTTP request/response and status codes
- Basic client–server architecture and JSON APIs
- Familiarity with asynchronous behavior (background requests, callbacks/promises)
- Basic understanding of reliability issues (timeouts, retries, duplicate requests)
What you'll learn
- Translate a product’s “instant” expectations into explicit freshness/update-cadence requirements and failure modes.
- Choose between polling, SSE, and WebSockets based on directionality, latency sensitivity, and operational constraints.
- Design a scalable update propagation approach using events and queues, and recognize overload/retry feedback loops.
- Implement safe retries using idempotency keys and understand when snapshotting reduces rebuild and resync costs.
- Ship optimistic UI flows that reconcile with authoritative server outcomes without double-apply or lost user input.
- Harden offline/reconnect behavior with exponential backoff plus jitter to avoid thundering herds.
- Explain how E2EE changes server responsibilities and still enables delivery UX, media transfer, and presence.
Learning path
7 modules • Each builds on the previous one
1
Latency budgets and real-time UX
Define what “instant” means (perceived latency budgets, jitter tolerance, update frequency) and how products like Uber, Figma, WhatsApp, and Notion map UX expectations to consistency guarantees (eventual, causal, strong) and failure modes.
1 video5 min
2
WebSockets vs polling vs SSE
Compare polling, long-polling, Server-Sent Events, and WebSockets for real-time updates: connection lifecycle, intermediaries (CDNs/proxies), mobile radio wakeups, heartbeats, and when to pick each.
3 videos16 min
3
Scaling fanout, presence, and backpressure
How “millions of updates per second” works: pub/sub, topic partitioning, sharding by geography, edge fanout, presence channels, rate limiting, backpressure, and delta compression for feeds and maps.
3 videos7 min
4
Ordering, versions, and idempotency
The primitives that make real-time safe: event IDs, Lamport/vector clocks (conceptually), causal ordering, deduplication, idempotent writes, exactly-once illusions, and checkpointing snapshots vs logs.
2 videos8 min
5
Optimistic UI updates and reconciliation
Make apps feel instant: local-first writes, speculative rendering, server acks, rollback vs forward-fix, conflict UI, and reconciling optimistic state with authoritative state under races and partial failure.
2 videos6 min
6
Offline sync and reconnection handling
Design for offline and flaky networks: local persistence, outbox/inbox queues, exponential backoff with jitter, resync strategies (diff, snapshot, log replay), conflict handling on reconnect, and reconnect storm mitigation.
2 videos7 min
7
Message delivery states with E2EE
Model WhatsApp-like messaging: sent/delivered/read semantics, device fanout, acknowledgements, ordering, retries, and how end-to-end encryption (e.g., Signal-style) constrains server visibility while preserving delivery UX.
3 videos11 min
Start Learning
Begin your learning journey
Modules7
Duration58 min
Science-backed learning
In-video quizzes and scaffolded content to maximize retention.
Key concepts
Freshness, Staleness, And Perceived Real-Time UXReal-Time Transport Selection: Polling Vs SSE Vs WebSocketsEvent-Driven Fanout And Queue-Based DecouplingOverload Dynamics, Retries, And Safe Deduplication With Idempotency KeysSnapshots And Log Replay Tradeoffs For State RebuildOptimistic UI Updates With Rollback/Retry ReconciliationOffline/Reconnect Strategy With Exponential Backoff And JitterE2EE Messaging Constraints, Media Delivery, And Presence Signals