gRPC and Event-Driven APIs

gRPC uses Protocol Buffers over HTTP/2 for efficient, strongly typed service-to-service calls with streaming and generated clients; browsers need gRPC-Web or a gateway. Event-driven APIs publish facts ("order.paid") to a broker; consumers react independently. Document async contracts with AsyncAPI and manage schemas (Avro/Protobuf/JSON Schema) with compatibility rules in a schema registry.

// orders.proto
syntax = "proto3";
package orders.v1;

service OrderService {
  rpc GetOrder(GetOrderRequest) returns (Order);
  rpc WatchOrder(GetOrderRequest) returns (stream OrderEvent);   // server streaming
}

message GetOrderRequest { string id = 1; }
message Order {
  string id = 1;
  string status = 2;
  int64 total_minor = 3;
  string currency = 4;
  // reserved 5; never reuse field numbers of removed fields
}

Common pitfalls

• Reusing or renumbering protobuf fields (breaks compatibility).
• Exposing gRPC directly to browsers without a gateway.
• Events that leak internal database structure.

Key points

• gRPC for typed internal RPC
• Events for decoupled reactions
• Schema evolution rules + registry

Further reading: gRPC introduction