gRPC Fundamentals

Internal service calls are different from public web APIs. They often happen many times per user request, have tight time limits, and may be used by services written in different languages. gRPC is built for that world.

In gRPC, you start by writing a .proto file. That file describes the service, its methods, and the messages those methods send and receive. Tools then generate client and server code from that file, so different teams and languages follow the same contract.

gRPC also gives you practical tools for production systems: deadlines, cancellation, metadata, status codes, and streaming. Metadata is extra call information, such as auth tokens, request IDs, or tracing headers.

REST and JSON are still excellent defaults, especially for public APIs and browser-facing APIs. gRPC shines when you control both sides of the API and want a strict contract between internal services.

This chapter explains how gRPC works, why teams use it, and when it is a better fit than REST.