gRPC vs REST

What’s the Difference Between gRPC and REST?

gRPC and REST are two ways you can design an API. An API is a mechanism that enables two software components to communicate with each other using a set of definitions and protocols. In gRPC, one component (the client) calls or invokes specific functions in another software component (the server). In REST, instead of calling functions, the client requests or updates data on the server.

What is gRPC?

gRPC is an open-source API architecture and system governed by the Cloud Native Computing Foundation. It’s based on the Remote Procedure Call (RPC) model. While the RPC model is broad, gRPC is a specific implementation.

What is RPC?

In RPC, client-server communications operate as if the client API requests were a local operation, or the request was internal server code.

In RPC, a client sends a request to a process on the server that is always listening for remote calls. In the request, it contains the server function to call, along with any parameters to pass. An RPC API uses a protocol like HTTP, TCP, or UDP as its underlying data exchange mechanism.

How is gRPC different from RPC?

gRPC is a system that implements traditional RPC with several optimizations. For instance, gRPC uses Protocol Buffers and HTTP 2 for data transmission.

It also abstracts the data exchange mechanism from the developer. For example, another widely used RPC API implementation, OpenAPI, requires developers to map RPC concepts to the HTTP protocol. But gRPC abstracts the underlying HTTP communication. These optimizations make gRPC faster, easier to implement, and more web-friendly than other RPC implementations.

What is REST?

REST is a software architecture approach that defines a set of rules to exchange data between software components. It’s based on HTTP, the standard communication protocol of the web. RESTful APIs manage communications between a client and a server through HTTP verbs, like POST, GET, PUT, and DELETE for create, read, update, and delete operations. The server-side resource is identified by a URL known as an endpoint.

REST works as follows:

1. The client makes a request to create, modify, or delete a resource on the server

2. The request contains the resource endpoint and may also include additional parameters

3. The server responds, returning the entire resource to the client once the operation is complete

4. The response contains data in JSON format and status codes

APIs built using REST guidelines are called RESTful APIs or REST APIs.

Why do organizations use gRPC and REST?

gRPC and REST are two different approaches to developing APIs.

An API operates similarly to ordering food from a restaurant via a menu. At any restaurant, a customer (client) can order food from the menu (API), which has a fixed set of dishes. This is communicated to the kitchen (server) that prepares the requested dish and sends it to the customer. The customer doesn’t need to know how the kitchen makes the order, only what to expect in return. The standardization of menu formats means customers and kitchens know how to use them.

Without APIs, there would be no shared agreement on how different applications or software services communicate. Programmers of two separate applications would need to speak to each other to determine how to build out the data exchange every time.

Different types of API architectures like gRPC and REST exist, as different ones can be better for different use cases within an organization. An API designer must choose their preferred client-server architecture based on system requirements.

What are the similarities between gRPC and REST?

REST and gRPC share some innate similarities as API architectural approaches.

Data exchange mechanism

Both allow two software components, a client and a server, to communicate and exchange data based on a shared set of rules. These rules apply regardless of how each software component operates internally.

HTTP-based communication

Both pass data via the HTTP request-response mechanism, the preferred efficient communication protocol of the web. However, in gRPC, this is hidden from the developer, while in REST, it’s more apparent.

Implementation flexibility

You can implement both REST and gRPC in a wide range of programming languages. This quality makes them both highly portable across programming environments. This leads to optimal interoperability with near-universal support.

Suitability for scalable, distributed systems

Both gRPC and REST use the following:

• Asynchronous communication, so the client and server can communicate without interrupting operations

• Stateless design, so the server doesn’t have to remember the client state

This means developers can use gRPC and REST to build fault-resistant systems with a large number of concurrent requests. You can build scalable, distributed systems with multiple clients.

Architecture principles: gRPC vs. REST

While REST and gRPC offer a similar function, the underlying models differ significantly in their architecture.

Communication model

Using a REST API, a client sends a single REST API request to a server, and the server then sends a single response in reply. The client must wait for the server to respond before continuing operations. This mechanism is a request-response model and is a unary data connection (one-to-one).

In contrast, with gRPC, a client can send one or multiple API requests to the server that may result in one or multiple replies from the server. Data connections may be unary (one-to-one), server-streaming (one-to-many), client-streaming (many-to-one), or bidirectional-streaming (many-to-many). This mechanism is a client-response communication model and is possible because gRPC is based on HTTP 2.

Callable operations on the server

In a gRPC API, callable server operations are defined by services, also known as functions or procedures. The gRPC client invokes these functions like you would call a function internally within an application. This is known as service-oriented design. Here’s an example:

createNewOrder(customer_id, item_id, item_quantity) -> order_id

In REST, there is a limited set of HTTP request verbs that the client can use on server resources defined by a URL. The client calls the resource itself. This is known as entity-oriented design. The entity-oriented design aligns well with object-oriented programming methods. Here’s an example:

POST /orders <headers> (customer_id, item_id, item_quantity) -> order_id

While you can design gRPC APIs in an entity-oriented approach, this is not a constraint of the system itself.

Data exchange format

With a REST API, the data structures passed between software components are typically expressed in JSON data exchange format. It is possible to pass other data formats like XML and HTML. JSON is easy to read and flexible, although it must be serialized and translated into a programming language.

In contrast, gRPC uses the Protocol Buffers (Protobuf) format by default, although it also offers native JSON support. The server defines a data structure using the Protocol Buffer interface description language (IDL) in a proto-specification file. gRPC then serializes the structure into binary format and then deserializes it to any specified programming language. This mechanism makes it faster than using JSON, which is not compressed during transmission. Protocol Buffers are not human-readable, unlike a REST API used with JSON.

Other key differences: gRPC vs. REST

Other key differences: gRPC vs. REST

Beyond architectural style, gRPC and REST have other inherent differences.

Client-server coupling

REST is loosely coupled, which means the client and the server do not need to know anything about the other's implementation. This loose coupling makes the API easier to evolve over time. This is because a change in server definitions does not necessarily require a code change in the client.

gRPC is tightly coupled, which means the client and server must have access to the same proto file. Any updates to the file require updates in both the server and the client.

Code generation

gRPC offers an inbuilt selection of client-side and server-side native code generation features. They’re available in multiple languages due to protoc, the Protocol Buffers compiler. After defining the structure in the proto file, gRPC generates the client-side and server-side code. Code generation makes API development less time-consuming.

On the other hand, REST does not offer any built-in code generation mechanisms, so developers must use additional third-party tools if they require this feature.

Bidirectional streaming

gRPC offers bidirectional streaming communication. This means both the client and the server can send and receive multiple requests and responses simultaneously on a single connection.

REST does not offer this feature.

When to use gRPC vs. REST

REST is currently the most popular API architecture for web services and microservice architectures. REST’s popularity is due to its simple implementation and data structure mapping, readability, and flexibility. It’s easy for new programmers to start developing RESTful APIs for their applications, whether for web services development or internal microservices.

Here are use cases for a REST API:

• Web-based architectures

• Public-facing APIs for ease of understanding by external users

• Simple data communications

gRPC, unlike REST, was designed specifically to allow developers to create high-performance APIs for microservice architectures across distributed data centers. It’s better suited for internal systems that require real-time streaming and large data loads. gRPC is also a good fit for microservice architectures comprising several programming languages when the API is unlikely to change over time.

A gRPC API is better for these use cases:

• High-performance systems

• High data loads

• Real-time or streaming applications

A note on web software development

While HTTP is the core web protocol, different versions of HTTP exist with varying degrees of adoption across web browsers and web servers.

A gRPC API always uses HTTP 2, and a REST API typically uses HTTP 1.1, which is not the same HTTP protocol. While HTTP 2 is now a common web protocol, it does not have universal browser support, unlike HTTP 1.1. This limited browser support can make gRPC a less attractive option for developers who want to support web applications.

Summary of differences: gRPC vs. REST

	gRPC API	REST API
What is it?	A system to create and use APIs based on the Remote Procedure Call (RPC) client-server communication model.	A set of rules that defines structured data exchange between a client and a server.
Design approach	Service-oriented design. The client asks the server to perform a service or function that may or may not impact server resources.	Entity-oriented design. The client asks the server to create, share, or modify resources.
Communication model	Multiple options like unary, one server to many clients, one client to many servers, and many clients to many servers.	Unary. A single client communicates with a single server.
Implementation	Requires gRPC software on both the client and server-side to operate.	You can implement it on the client and server-side in a wide variety of formats with no common software necessary.
Data access	Service (function) calls.	Multiple endpoints in the form of URLs to define resources.
Data returned	In the fixed return type of the service as defined in the Protocol Buffer file.	In a fixed structure (typically JSON), defined by the server.
Client-server coupling	Tightly coupled. Both client and server need the same Protocol Buffer file that defines the data format.	Loosely coupled. Client and server are not aware about internal details.
Automatic code generation	Built-in feature.	Requires third-party tools.
Bidirectional streaming	Present.	Not present.
Best suited for	High-performance or data-heavy microservice architectures.	Simple data sources where resources are well-defined.