Building real-time chat systems
The boring infrastructure details that make chat feel instant: ordering, retries, backpressure, presence, and delivery state.
Real-time is a contract
Users do not care whether a message moved through websockets, queues, or database triggers. They care that it arrives quickly, appears once, and does not reorder itself into nonsense.
That means real-time systems need a contract for ordering, retries, and idempotency before they need fancy live features.
Backpressure matters early
Mobile clients disconnect. Networks stall. Users send bursts. Translation or moderation pipelines take time.
If every stage assumes the next one is always ready, the system will eventually punish the user for normal behavior.
Presence is product design
Online indicators, typing states, read receipts, and delivery ticks are not just backend events. They shape trust.
A good chat system chooses which signals are worth showing and which ones should stay invisible.