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Lessons (6)

• Distributed Coordination: Consensus, Heartbeats and Gossip

  … leader agreement, heartbeats, gossip membership and checksums solve different failure questions](/img/system-design-l6/coordination.svg) Problem …

• Design a Chat Application

  … Presence is temporary state with TTL heartbeats; delivery and read receipts are durable state transitions. Offline push comes …

• Premiere-Night Video Streaming

  … degradation: cap bitrate, disable previews, or queue sessions. Heartbeat progress to Redis for fast resume and persist asynchronously …

• API Gateway, BFF & Service Discovery

  … O1[orders instance 1] -- register + heartbeat Registry O2[orders instance 2] -- register + heartbeat Registry C[Checkout svc] -- "where …

• Consumers & Consumer Groups

  … stops sending heartbeats 💀 GC- C1: rebalance! Note over C1: C1 now has P0, P1, P2, P3 Note over …

• Brokers, Replication & Durability

  … detects missing heartbeats C- B2: you are the new leader of P0 👑 P- B2: producer refreshes metadata, keeps …