How can services interact with each other? How does REST differ from gRPC?

Services can interact with each other through various protocols and approaches, for example:

• HTTP/REST — data exchange via HTTP requests using standard methods (GET, POST, etc.) and formats (JSON, XML).
• gRPC — a high-performance remote procedure call (RPC) framework using the HTTP/2 protocol and binary protobuf format.
• Messages through brokers (RabbitMQ, Kafka) — asynchronous interaction.
• WebSocket — bidirectional real-time communication.

Differences between REST and gRPC:

Characteristic	REST	gRPC
Protocol	HTTP/1.1	HTTP/2
Message format	Text-based (usually JSON)	Binary (Protocol Buffers)
Performance	Lower due to text format and lack of multiplexing	Higher thanks to binary format and HTTP/2 multiplexing
Language support	Wide, any language with an HTTP client	Wide, but requires code generation from proto files
Approach	Resource-oriented	Operation-oriented (RPC)

Example of a REST call:

GET /users/123 HTTP/1.1
Host: example.com

gRPC example (in Go):

client := pb.NewUserServiceClient(conn)
resp, err := client.GetUser(ctx, &pb.GetUserRequest{Id: "123"})

Choosing between REST and gRPC depends on performance requirements, compatibility, and system architecture.