ADR-003: Protocol Introduction Order
Order
- REST + Postgres
- Kafka events
- gRPC (inventory)
- WebSocket (notifications)
- GraphQL
- SSE (feed / flash sale)
- SOAP (payment)
- Webhooks + RabbitMQ
- MQTT (IoT)
- Streams / Batch
- Multi-region replication
- mTLS / OPA / Vault advanced
Rationale
Reduce cognitive overload; each milestone adds one new major protocol.