Message Center - Redesigning the messaging experience on the Grab superapp

Summary

Grab redesigned its messaging infrastructure from GrabChat to Message Center to overcome two-party chat limitations and support complex superapp requirements like group conversations and varied user roles. The architecture separates core processing logic from message delivery by splitting the system into a backend processor and an independently scalable postman service. Communication relies on an in-house TCP gateway named Hermes that proxies client payloads via gRPC, alongside Apache Kafka streams and Amazon SQS delay queues. Custom client-server acknowledgements and a DynamoDB event store ensure reliable message delivery even across dropped mobile TCP connections and offline reconnects.

Takeaways

1. 1

   Decoupling the message processing backend from the postman delivery service enables message delivery to scale independently when group chats multiply outbound message volume.

2. 2

   Because standard TCP packets lack inherent application-layer response guarantees, a bidirectional ACK system with idempotent event IDs is necessary to verify delivery and avoid cascading retry loops.

3. 3

   When client TCP connections drop, Message Center triggers push notifications via Hedwig and records pending events in DynamoDB, replaying undelivered messages once the client reconnects and notifies Hermes.