REST (Representational State Transfer) APIs have become the standard for building APIs that allow different software systems to communicate and share data over the internet. The purpose of using REST APIs is to create a simple, lightweight and scalable architecture for accessing resources and services over HTTP.
What is a REST API?
A REST API is an application programming interface (API) that uses HTTP requests to GET, PUT, POST and DELETE data. REST, or RESTful APIs, provide interoperability between computer systems on the internet by adhering to REST architectural constraints. They typically work by accessing resources using URLs that specify the method and format of requests and responses.
For example, a GET request might retrieve information for a specific customer, while a PUT request might update that customer’s information. REST APIs use standard HTTP methods, status codes and headers to serve information in a simple and scalable way.
Key Principles of REST APIs
REST APIs aim to capture the characteristics of the web including its architecture, performance, scalability and simplicity. They follow a set of guiding principles:
- Client-server – There should be a separation between the client requesting information and the server that provides resources. This improves scalability and user interface portability.
- Statelessness – No client information is stored on the server between requests. Each request contains all the information needed to complete it.
- Cacheable – REST responses should indicate if they are cacheable to improve performance.
- Uniform interface – Using standard HTTP methods to access and manipulate resources.
- Layered system – Clients cannot tell if they are connected directly to the server or going through intermediaries like proxies.
Benefits of Using REST APIs
There are many benefits to building APIs using the REST architectural style:
Simplicity
REST APIs use existing HTTP methods like GET, POST, PUT and DELETE to perform operations on resources. This is straightforward and easy to understand.
Flexibility
REST allows different data formats like JSON, XML, YAML, etc. Developers have the flexibility to choose formats that work for their needs.
Scalability
The separation of client and server and stateless nature of REST makes REST APIs very scalable. Servers don’t have to retain client state between requests.
Visibility and Portability
REST uses standards like HTTP, URI, JSON and XML making APIs portable across different languages, platforms and devices. The use of URLs also helps to identify resources and route requests.
Reliability
REST APIs provide reliable performance by building on existing HTTP infrastructure such as caching, authentication, authorization and headers.
Modifiability
New functionality can be added to REST APIs without breaking existing clients by using new URLs, response codes or properties. Old APIs can also be deprecated if needed.
Common Uses of REST APIs
Here are some common uses and examples of REST APIs in real-world applications:
Public APIs
Many popular web services provide public REST APIs that allow developers to integrate their data into other applications. Examples include:
- Twitter API
- Stripe API
- Facebook Graph API
- GitHub API
Internal APIs
REST APIs are commonly used internally within organizations to build modular application components that can be reused and accessed by other systems:
- User management APIs
- Product catalog APIs
- Order processing APIs
- Payment APIs
Mobile Applications
Mobile apps often use REST APIs to integrate and exchange data with backend systems. For example:
- A weather app using APIs to access weather data
- A social app using APIs to interface with the service’s platform
- A banking app using APIs to retrieve accounts, transfer funds, etc.
Web Applications
Websites and web apps make use of REST APIs to perform server-side logic and retrieve resources to populate the user interface. Common examples include:
- Content APIs to manage and query content in a CMS
- User profile APIs
- Shopping cart and order processing APIs
- Payment gateway APIs
Internet of Things
REST APIs are simple and lightweight enough to be used on IoT devices with limited resources. For example:
- APIs on home automation devices to remotely control lighting, temperature, etc.
- APIs on wearables to send biometric data to apps
- APIs on industrial equipment like wind turbines to monitor performance
Comparison to Other API Styles
REST is one popular architectural style for building web APIs. But there are other styles that work better in certain situations:
GraphQL
GraphQL is an alternative to REST for building APIs focused on giving consumers greater control and efficiency. Clients can specify exactly what data they need in a query instead of fetching from fixed endpoints.
SOAP
SOAP is a protocol for building APIs focused on formal contracts, security, transactions and ACID compliance. It defines strict standards and is commonly used internally by enterprises.
gRPC
gRPC uses HTTP/2, protobuf and provides lower latency by using binary serialization. It is a popular choice for internal microservices and systems that require high performance.
WebSocket
WebSocket provides full-duplex communication channels over a single TCP connection. It is useful for applications that require continuous real-time data transfer like chat, streaming, etc.
In summary, REST provides a great balance of simplicity, flexibility and scalability for most common web API scenarios. But other styles have benefits for specific use cases.
Challenges of REST APIs
While REST is popular, it also comes with some challenges to be aware of:
Over-fetching data
REST APIs tend to over-fetch information since clients receive a fixed data structure per request. This can result in large payloads of unnecessary information.
Versioning
When REST APIs need to evolve, new API versions have to be handled carefully without breaking existing clients. This can add complexity.
Chatty interfaces
Fetching nested or related resources may require multiple round trips between client and server, adding latency.
Caching issues
REST caching is complex to implement correctly. Mismanaging cache invalidation can cause major problems.
Stateful interactions
REST requires state to be handled on the client side since servers are stateless. This can complicate certain interactions.
Best Practices for REST APIs
Here are some best practices to follow when designing REST APIs:
Use HTTP Methods correctly
- GET – Retrieve a resource
- POST – Create a resource
- PUT – Update a resource
- DELETE – Delete a resource
Use logical, consistent URLs and naming
- E.g. /users, /users/123, /orders
- Keeps URLs and routes easy to understand and maintain
Use nouns over verbs in URLs
- Nouns identify resources while verbs focus on actions
- E.g. /accounts over /getAccounts
Respond with standard status codes
- 200 OK, 400 Bad Request, 401 Unauthorized, etc.
- Helps clients understand responses and react properly
Provide sufficient metadata
- E.g. Content-Type, Content-Length, Last-Modified headers
- Enables caching and conveys important information to clients
Allow filtering, sorting, pagination
- Support query params for filtering large collections of resources
- Page results using limit and offset to avoid huge responses
Handle errors gracefully
- Use codes like 400, 401, 403, 404, 500
- Return error details in response body
- Log errors and notify developers of issues
Document API thoroughly
- Specify request/response formats, error codes, authentication, etc.
- Use Open API, Swagger, RAML or API Blueprint
- Include code samples and tutorials for clients
Support backward compatibility when possible
- Avoid breaking changes to existing APIs
- Deprecate APIs before removing them
- Version APIs when necessary for large changes
Conclusion
REST APIs offer simple, scalable and flexible architecture for accessing resources over HTTP. They have become the standard for building APIs thanks to their separation of client and server, stateless nature, use of common HTTP methods and support for different data formats.
REST APIs are useful in providing public web services, enabling internal system integration, powering mobile apps, delivering web content and connecting Internet of Things devices. While REST has some drawbacks like over-fetching and versioning issues, applying best practices around URLs, HTTP verbs, status codes, metadata and error handling can help create clean, maintainable interfaces.
Understanding the principles, benefits and challenges of REST APIs provides the knowledge to decide when to use REST and how to design quality, effective RESTful interfaces.
