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System Design · Module 7 of 10

APIs and communication

Design how services talk to each other.

📖 Key ideas

  1. REST over HTTP is the most common API style.
  2. gRPC uses Protocol Buffers for fast service-to-service calls.
  3. GraphQL lets clients request exact data.
  4. WebSockets enable real-time two-way communication.
  5. API gateways handle routing, auth and rate limiting.
💡 Real-life example: An API gateway is a building reception routing visitors to the right office and checking their passes.
RESTResource-based HTTP API style
gRPCHigh-performance RPC framework
WebSocketPersistent two-way connection
API gatewaySingle entry point for APIs