gRPC vs REST for Model Serving

A serving API defines how clients submit inputs, receive predictions, handle errors, and evolve versions. REST usually refers to resource-oriented HTTP interfaces, commonly with JSON request and response bodies. This style is broadly supported by browsers, command-line tools, proxies, and API gateways. It can be easy to inspect and debug, though large nested numeric payloads in JSON may be verbose and require conversion. gRPC is an RPC framework in which services and methods are defined in protocol files. It commonly uses Protocol Buffers for typed message serialization and generates client and server code. The framework supports unary calls and streaming patterns, and uses HTTP/2 transport. Binary messages can be compact and efficient for structured data, but clients need compatible generated code or libraries, and some browser or proxy environments require additional components. Neither interface is automatically faster in every deployment. Serialization cost, payload size, compression, connection reuse, TLS, network distance, client implementation, and server processing all matter. Model inference itself may dominate total time, making protocol differences negligible. Measure end-to-end latency and throughput under the real request mix. Schema evolution requires care. Protocol Buffers assign field numbers and have compatibility rules; REST JSON also needs documented versioning and validation. Avoid reusing removed field identifiers or changing units silently. For both, define request limits, deadlines, authentication, retries, idempotency, error codes, and observability. Large image and audio data may be sent as binary, uploaded separately, or referenced by object storage, depending on security and size constraints. Choose based on ecosystem and use case. A public client interface may favor HTTP and JSON simplicity; tightly controlled internal services with typed schemas or streaming needs may favor gRPC. Keep model preprocessing and prediction semantics consistent regardless of transport, and test compatibility across client versions.