System Design
Advanced
Design Global Chat and Messaging
Build durable messaging with presence, ordering, offline delivery, and cross-region scale.
45 min
3 sections
chat
messaging
multi-region
1
2
3
01. Separate message durability from connection state
Section 1 of 3
Messages belong in durable storage. WebSocket gateways manage online connections and ephemeral presence. This separation lets users reconnect, sync missed messages, and move between devices.
text
Message send:
Client -> regional gateway
-> auth and conversation membership check
-> message service assigns sequence
-> durable write
-> event stream
-> fanout to online devices
-> push notification for offline devicesBack to Course