REST vs gRPC: Which API Architecture Wins for Modern Microservices?

What Is an API?

An API (Application Programming Interface) acts as a mediator between software components, defining how requests and responses are exchanged.

The API works by sending a user request from a client (e.g., a hotel‑booking webpage) to a server, which processes the request and returns a response that the client displays.

API and Microservices

In monolithic applications all functionality resides in a single codebase, whereas microservice architectures consist of many small services that communicate via HTTP‑based APIs, enabling independent development and deployment.

Common API styles include RPC, REST, and GraphQL; this article focuses on RPC (gRPC) and REST.

What Is RPC?

Remote Procedure Call (RPC) uses a client‑server model where the client sends a request that the server processes and returns a response, blocking the client until completion. RPC defines how functions are invoked remotely and supports both local and distributed environments.

What Is REST?

REST (Representational State Transfer) APIs expose resources that can be accessed via standard HTTP verbs (GET, POST, PUT, DELETE) and typically exchange data in JSON or XML formats.

What Is gRPC?

gRPC (Google Remote Procedure Call) is an RPC framework built on HTTP/2. It hides HTTP details from developers, reducing complexity, and uses Protocol Buffers (Protobuf) as its default IDL for defining services and messages.

gRPC offers built‑in code generation via the protoc compiler, supporting many programming languages.

gRPC vs REST Comparison

HTTP 1.1 vs HTTP 2.0

REST typically runs on HTTP 1.1, handling one request at a time per connection, while gRPC leverages HTTP 2 to enable multiplexed, bidirectional streaming and handle multiple concurrent requests efficiently.

Data Stream Types

Unary: single request‑response

Server streaming: server sends a stream of messages

Client streaming: client sends a stream of messages

Bidirectional streaming: both sides exchange streams independently

Browser Support

All browsers natively support REST, whereas gRPC requires gRPC‑Web and a proxy to translate between HTTP 1.1 and HTTP 2, limiting its use to internal or private systems.

Payload Data Structure

gRPC uses binary Protobuf messages, which are compact and strongly typed, while REST relies on JSON or XML, which are text‑based, human‑readable, but larger and require additional serialization overhead.

Code Generation

gRPC provides native code generation via protoc, simplifying SDK creation, whereas REST APIs typically need third‑party tools like Swagger or Postman to generate client code.

Feature Comparison

HTTP Protocol: gRPC uses HTTP 2; REST uses HTTP 1.1.

Message Format: gRPC – Protobuf; REST – JSON/XML.

Code Generation: gRPC – native compiler; REST – external tools.

Communication Model: gRPC supports unary, streaming, and bidirectional calls; REST supports simple request‑response.

Execution Time (example): gRPC – 45 minutes; REST – 10 minutes (illustrative).

When to Use gRPC vs REST

gRPC excels in internal, high‑performance, multi‑language environments, IoT systems, and mobile apps where low latency and small payloads matter. REST remains the universal choice for public web services due to its broad browser support and mature ecosystem.

Conclusion

gRPC offers performance, streaming, and strong typing advantages, especially with HTTP 2 and Protobuf, but its limited browser compatibility makes REST the more practical default for most web‑based microservice integrations.