Designing a Real-Time Chat System at Scale

Short summary

A scalable chat system requires WebSocket persistence, durable message storage before publishing, and per-conversation ordering. Production systems solve write bottlenecks via Kafka streams and conversation-based sharding. Building real-time messaging at scale transforms a UI feature into a distributed systems problem requiring gateway clusters, failure recovery, and global latency management.

• •Production chat needs WebSockets, persistent connections, and durable storage before publishing
• •Message ordering is per-conversation; scaling uses Kafka, Redis Streams, and sharding by conversation_id
• •Distributed systems concerns dominate: gateway clusters, fault tolerance, multi-device sync, global latency

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