gRPC

gRPC is a high-performance, language-agnostic RPC framework originally developed at Google that uses Protocol Buffers (protobuf) as its interface definition language and serialization format, and HTTP/2 as its transport protocol. It supports four communication patterns: unary (request-response), server streaming, client streaming, and bidirectional streaming. gRPC is primarily used for internal service-to-service communication in microservice architectures where performance, strong typing, and code generation are priorities.

Protocol Buffers define the service contract in .proto files, specifying services, methods, and message types with field numbers for efficient binary serialization. The protoc compiler generates client stubs and server interfaces in multiple languages (Go, Java, Python, C++, Node.js, etc.), ensuring type safety across service boundaries. Binary serialization is significantly more compact and faster to parse than JSON, reducing network bandwidth and CPU usage -- critical for high-throughput internal APIs.

gRPC's HTTP/2 foundation provides multiplexing (multiple concurrent RPCs on a single connection), header compression (HPACK), and flow control. Streaming support enables efficient patterns like real-time data feeds and progressive uploads. However, gRPC isn't natively supported in browsers (requiring gRPC-Web as a translation layer), and its binary protocol makes debugging harder than JSON-based REST APIs. It's typically deployed behind an API gateway that translates external REST/JSON requests to internal gRPC calls, combining the developer-friendliness of REST for external consumers with the performance of gRPC internally.