REST (Representational State Transfer) APIs have become the standard for building API services. REST APIs provide a simple, easy to understand way to organize and structure an API using HTTP methods like GET, POST, PUT, and DELETE to manipulate resources. Some of the main benefits of REST APIs include:
Simplicity
REST APIs use basic HTTP methods and are designed to be simple, lightweight, and easy to understand. There is less overhead compared to other protocols like SOAP. The resources are identified through URIs and manipulated using standard HTTP methods. This makes REST APIs very intuitive and easy for developers to work with.
Flexibility
REST APIs provide a lot of flexibility. Data is not tied to methods and resources. Developers have the freedom to represent resources in a variety of formats like JSON, XML, YAML, etc. It is also easy to version REST APIs and evolve them over time without breaking existing clients.
Scalability
REST is designed to use a stateless client-server protocol. This makes REST APIs highly scalable since the server does not need to retain client state between requests. The client includes all the necessary information in each request. Load balancers can distribute requests across multiple servers to handle any load. Caching improves performance and scalability.
Reliability
REST APIs use HTTP which is reliable and resilient to network failures. If a request fails, it can simply be sent again. HTTP has error handling built-in with status codes to indicate failures. This provides reliability and the ability to handle errors gracefully.
Performance
REST APIs provide good performance since they are built on top of HTTP. HTTP is a mature protocol that has been optimized over the years for fast network communication. REST allows leveraging existing HTTP infrastructure like caching, connection pooling, compression, etc. to improve performance.
Main Use Cases
Given their advantages, REST APIs are commonly used in the following scenarios:
Public APIs
REST APIs make for great public APIs. Their simplicity makes them easy for other teams and developers to understand and consume. Versioning helps avoid breaking changes for existing consumers. Public REST APIs are provided by many cloud services like AWS, Google Cloud, Stripe, etc.
Microservices
Microservices architecture relies on APIs for communication between the services. Since microservices are independently deployable and scaled, they need an API that is flexible, reliable and scalable. REST APIs are a great fit due to their advantages. Most microservices expose APIs using REST principles.
Mobile Apps
Mobile apps need to fetch data and communicate with backend services. REST APIs work well for mobile apps due to their small payload sizes, use of HTTP for reliability, and ability to be cached on the client-side. Most mobile apps use REST APIs to connect to their backend.
Web Applications
Web applications need to load data asynchronously from the backend without page refreshes. REST APIs enable this by allowing JavaScript clients to directly call API endpoints to fetch or modify data. The data can then be used to update parts of the UI without reloading the entire page.
Enterprise Integration
Within large enterprises, REST APIs provide a simple way to open up data and functionality from legacy systems. By exposing stable REST APIs, other systems can easily consume those capabilities in a standardized way. This helps integrate otherwise disconnected systems.
Common REST API Architectural Constraints
While REST APIs provide a lot of flexibility, there are some common architectural constraints that are followed to adhere to REST principles:
Client-Server
There should be a clear separation between clients and servers. Servers manage application state and handle API requests. Clients are not concerned with data storage and only interact with APIs.
Stateless
No client session state is stored on the server. All session state is handled on the client. Each request from the client must contain all the necessary information required to process it.
Cacheable
REST responses should ideally be cacheable to improve performance. Well-managed caching reduces client-server interactions and improves scalability.
Uniform Interface
A uniform interface is used consisting of resources, representations, and HTTP methods like GET, POST, PUT, DELETE, etc. This defines how clients interact with the endpoints.
Layered System
Clients only interact with the API layer. Servers can call other services to implement functionality. This provides abstraction and encapsulation.
Code on Demand (Optional)
REST APIs may optionally return executable code to extend client functionality. This enables clients to execute logic using the downloaded code.
REST API Best Practices
Here are some best practices to follow when designing REST APIs:
- Use logical, meaningful and consistent resource naming. For example, use /users instead of /getAllUsers.
- Keep URLs and payloads as small as possible by avoiding unneeded information
- Always use HTTPS for security
- Provide full support for HTTP methods like GET, POST, PUT, DELETE
- Use HATEOAS to include links and related information in payload
- Always return appropriate HTTP status codes
- Properly version APIs and avoid breaking changes for existing consumers
Common Protocols Used with REST APIs
While the REST APIs themselves are protocol agnostic, there are some common protocols used in conjunction with them:
HTTP
Hypertext Transfer Protocol is the core protocol used for REST API communication over the web. HTTP establishes the connection and provides headers, status codes, caching, etc.
JSON
JavaScript Object Notation is the most popular format for serializing and transmitting data through REST APIs. JSON is lightweight text-based and easy for clients to parse.
XML
Extensible Markup Language is another common data format supported by REST APIs. XML provides more structure and validation than JSON but creates larger payloads.
WebSocket
WebSocket protocol enables persistent, bidirectional streams of data over REST APIs. This allows servers to push data to clients when an event occurs.
OAuth 2.0
OAuth 2.0 framework enables authorization flows for secure user login and API access control. It provides different grants to get access tokens.
How REST APIs Compare to SOAP
SOAP and REST APIs both allow accessing web services over HTTP. However, there are some key differences between the two:
| Criteria | SOAP | REST |
|---|---|---|
| Protocol | SOAP | HTTP |
| Messaging Format | XML | JSON, XML, etc. |
| Caching | Difficult to cache | Easy to cache |
| Standards | WS-* standards | No standards |
| Complexity | More complex | Very simple |
| Payload Size | Tends to be larger | Lightweight, smaller |
As seen from the comparison, SOAP has more rigid standards whereas REST APIs are designed for simplicity and flexibility. For most common web API use cases today, REST APIs are preferred.
Conclusion
REST APIs have become ubiquitous for building scalable and easy to use web services. Their advantages like simplicity, flexibility and broad adoption make them ideal for public APIs, microservices, web apps, mobile apps and enterprise integration use cases. By following REST constraints and best practices, high quality and robust APIs can be built. With widespread tooling and community support, REST has become the standard for web APIs today.