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How the REST API should be designed?

Designing a well-structured REST (REpresentational State Transfer) API is essential for building an effective web service. A REST API allows client applications to access and manipulate resources hosted on a server over the HTTP protocol. When designed correctly, a REST API provides a great developer experience and enables services to scale well. This article will provide guidelines and best practices for designing a comprehensive, consistent, and robust REST API.

What is REST and RESTful API Design?

REST is an architectural style for building distributed systems based on hypermedia. REST aims to create lightweight and maintainable web services that provide a uniform interface between the client and the server. A RESTful API conforms to the principles and constraints of REST architecture:

  • Client-server separation – Client and server act independently
  • Statelessness – No client session data is stored on the server between requests
  • Cacheability – Responses indicate if they can be cached to improve performance
  • Layered system – Requests/responses go through layers like load balancers, caches, etc.
  • Uniform interface – Resources are uniquely identified using URIs
  • Code-on-demand (optional) – Ability to send executable code from server to client

RESTful API design refers to the process of designing HTTP interfaces that adhere to the REST architecture constraints. The goal is to create APIs that are simple, lightweight, scalable and easy to use and maintain in the long run.

Why Use a RESTful API?

There are several key advantages of using a well-designed RESTful API:

  • Separation of client and server: The API allows for independent evolution of client and server applications.
  • Visibility, reliability, scalability: REST uses HTTP and HTTPS which are familiar internet protocols and allow reuse of existing infrastructure.
  • Lightweight and fast performance: No bulky protocols or inefficient abstractions.
  • Good fit for internet scale: REST naturally works well for building web-scale solutions.
  • Simplicity and flexibility: Human readable URLs, use of HTTP methods, self-descriptive error messages.
  • Easy to implement: No complex tooling required. Any HTTP library can be used.

Overall, a REST API aims to provide a clean, lightweight and fast interface between systems and scale across the internet.

Best Practices for Designing a REST API

Here are some key best practices and guidelines to follow when designing a REST API:

Use HTTP Methods Properly

HTTP verbs like GET, POST, PUT, PATCH and DELETE should be used properly to take advantage of their semantics:

  • GET – Used for retrieving resources. Should not modify any resources.
  • POST – Used for creating new resources. For example creating a new user.
  • PUT/PATCH – Used for updating existing resources. For example updating an existing user profile.
  • DELETE – Used for deleting resources.

Use Logical Nesting of Resources

Resources should be nested logically under one another:

/users
/users/123
/users/123/orders
/users/123/orders/15

This helps keep the URI scheme intuitive and easy to understand.

Use Plural Nouns for Resources

Resource names in URIs should be plural nouns. For example:

/users 
/photos
/products 

Keeping resource names consistent and meaningful helps developers quickly understand what your API provides access to.

Use Sub-Resources for Relations

Use sub-resources to represent relations between resources. For example:

/users/123/orders - Get orders for user 123
/orders/15/items - Get items for order 15

This is a clean way to represent resource relationships.

Use HTTP Status Codes

HTTP status codes like 200, 400, 401, 403 etc. should be leveraged to indicate request status and errors.

Provide Complete Documentation

Great documentation is crucial for developer adoption. At minimum provide:

  • Overview of API capabilities and use cases
  • Sample requests and responses
  • Authentication methods
  • Error codes and messages
  • Code samples in multiple languages
  • Interactive documentation using OpenAPI

Provide Versioning

Version your API using urls, request headers or media type versioning. Example:

https://api.domain.com/v1/users
https://api.domain.com/v2/users 

This allows easy upgrading/iteration of your API over time without breaking backwards compatibility.

Follow Standard API Conventions

Where possible, follow standard conventions used by popular APIs like:

  • Return JSON data
  • Accept JSON encoded data
  • Use HTTP authentication and standard OAuth flows
  • Allow cross-origin resource sharing (CORS) for AJAX requests
  • Follow other general web API standards

This helps build developer trust and makes your API more intuitive.

Provide Filtering, Sorting, and Pagination

Add query parameters that allow filtering, sorting, and pagination. For example:

/users?limit=25&offset=50 - Get 25 users after skipping 50
/users?sort=lastname - Sort users by last name
/users?firstname=John - Filter users by first name

This allows developers to efficiently query and manipulate resources.

Enable Caching

Set HTTP cache headers like Cache-Control, Expires and ETag to improve performance. This allows caching of resources to avoid re-fetching unchanged data.

Rate Limiting

Implement rate limiting to prevent abuse and improve stability under high traffic. This is done by limiting number of requests per hour/day from a single IP address or user.

Monitor API Usage

Track API request counts, response times, errors etc. to monitor API usage and performance. Quickly detect bugs or abuse and improve API quality over time.

Common Design Patterns

Here are some commonly used design patterns when building REST APIs:

Collection Pattern

Use a collection resource to represent a collection of subordinate resources. For example:

GET /users - Get a list of users
POST /users - Create a new user

Controller Pattern

Use a controller resource to handle business logic between a client request and subordinate resources. For example:

POST /users/123/placeOrder - Place an order for user 123

Utility Pattern

Use a utility resource to perform an operation across multiple resources. For example:

GET /search?name=John - Search for user with name John

Repository Pattern

Create a repository resource to allow manipulation of a data store through a collection-like interface. For example:

  
GET /users - Get list of users
POST /users - Create a new user
GET /users/123 - Get user with ID 123
PUT /users/123 - Update user with ID 123
DELETE /users/123 - Delete user with ID 123

The repository pattern is very common since it directly mirrors database-style operations.

Common Design Mistakes

Some common mistakes to avoid when designing a REST API:

  • Not using HTTP verbs and status codes properly
  • Nested resources too deeply with complex URI scheme
  • Trying to design a “perfect” API the first time – it will evolve over time
  • Not providing versioning support
  • Not documenting the API properly
  • Not following consistent naming conventions
  • Not monitoring API usage, errors, latency
  • Not adding API security like authentication, rate limiting, CORS

REST API Design Tools

There are many useful tools for designing, prototyping, testing and publishing REST APIs:

  • Swagger / OpenAPI – Design, document, and generate clients for your API
  • Postman – Test and iterate on your API endpoints
  • API Blueprint / RAML – Create API specifications and documentation
  • Mock servers – Simulation of production API for testing
  • API Gateways – Tools like Kong, Tyk and APIGee for security, traffic control, analytics

Conclusion

Designing an excellent REST API that meets your project needs takes skill and experience. Follow common best practices, patterns and tooling to create an API that is easy to use and maintainable in the long run. Keep iterating and improving your API over time as its usage grows. Building a REST API can be challenging but also very rewarding when done right!