- 5 Key Principles of REST APIs
- Uniform Interface
- Client-Server Design Pattern
- Layered System
- Stateful and Stateless Protocols
- Limitations of Stateful APIs
- Why Are REST APIs Stateless?
- Best Practices for Adopting REST APIs
- Use JSON
- Use Nouns Instead of Verbs in URL
- Error Handling
- Well-Compiled Documentation
- Allow Sorting, Filtering, and Pagination
- Bottom Line
REST APIs dominate API development today. Most of the APIs are developed using the REST architecture for a variety of reasons, such as simplified development, easy to understand architecture, great support available online, and wide acceptance from developers and organizations around the world. In this article, we’ll discuss what makes REST APIs so popular, along with their salient features.
REST (representational state transfer) is an architectural style that defines certain constraints to be followed in web service development. A REST API is an application programming interface that obeys REST constraints and therefore enables seamless communication with RESTful web services. REST is simple, flexible, and requires less bandwidth, making it ideal for usage on the internet. All communication done via the REST API uses only HTTP requests.
5 Key Principles of REST APIs
REST imposes certain architectural constraints on APIs. The five major guiding principles or constraints of REST are: uniform interface, stateless, cacheable, client-server, and layered system.
This is a fundamental principle for the design of any RESTful API. There should be a uniform and standard way of interacting with a given server for all client types. The uniform interface helps to simplify the overall architecture of the system.
The constraints that help achieve this include:
Identification of resources: Every system resource should be uniquely identifiable, by using a Uniform Resource Identifier (URI).
Manipulation of resources through representations: Clients should get a uniform representation of a resource that contains enough information to modify the resource's state in the server, as long as they have the required permissions.
Self-descriptive messages: Every resource representation should provide enough information for the client to know how to process it further, such as additional actions that can be performed on the resource.
Hypermedia as the engine of application state (HATEOAS): Clients should have enough information, in the form of hyperlinks, to dynamically discover other resources and drive other interactions.
REST architecture mandates that the server will not store anything related to a session. The server should process and complete each request independently. Each client request should contain all of the information necessary for understanding, processing, and completing it. Clients can do this via query parameters, headers, URIs, request body, etc. This principle of stateless versus stateful web app design will be discussed in more detail below.
Every response sent by the server should contain information regarding its cacheability. Simply, the clients should be able to determine whether or not this response can be cached from their side, and if so, for how long. If a response is cacheable, the client has the right to return the data from its cache for an equivalent request and specified period, without sending another request to the server. A well-managed caching mechanism greatly improves the availability and performance of an API by completely or partially eliminating some of the client-server interactions. However, this increases the chances of users receiving stale data.
Client-Server Design Pattern
REST architecture imposes the client-server design pattern, which enforces the separation of concerns and helps the client and server function independently. In REST, a client is an entity that requests a resource. A server is an entity responsible for storing these resources, having business logic, and sending the response to the client. In many cases, one server (API) can have multiple clients using different client-side technologies, or even other servers that act as a client of the API.
An application with layered architecture is composed of various hierarchical layers. Each layer has information from only itself, and no other layer. There can be multiple intermediate layers between the client and server. You can design your REST APIs with multiple layers, each having tasks such as security, business logic, and application, all working together to fulfill client requests. These layers are invisible to the client and only interact with intermediate servers. This architecture improves the overall system availability and performance by enabling load balancing and shared caches.
Stateful and Stateless Protocols
We have already discussed what stateless protocol is. Now let’s discuss stateful protocol. The main difference between stateful and stateless protocol is that in stateful protocol, the server maintains the state of its sessions (e.g., authentication sessions or the client’s previous requests). This information can be used repeatedly for future requests. The same server is used to serve each request in a session. This means that when using stateful protocols, we should always consider the cost associated with it. Also, this is one reason why stateful is not recommended for modern applications.
Limitations of Stateful APIs
The stateful protocol does comes with some serious limitations and disadvantages:
Requires storage, since the stateful protocol stores session data, in-memory storage or a database is required to store these sessions. If we use in-memory storage, then requests from the same sessions must be sent to the same server every time. Also, if that server is down, all the session data is lost, and subsequent requests from the same session can’t be served.
Heavily dependent on the server-side state, because if the server loses the stored information, the request cannot be correctly processed.
Backing storage is often needed because of this server-side state dependence.
Overall performance decreases if the session is not efficiently managed.
Scaling a stateful API is a complex and difficult process, as the state of some of the requests might be stored on a particular server. Therefore, we need subsequent requests from the same client to go to the same server. This makes load balancing of requests more difficult as well.
Why Are REST APIs Stateless?
As discussed above, one constraint of REST API architecture is that it must be stateless. Stateless APIs offer multiple advantages:
Helps improve the scalability of APIs to millions of concurrent users: Statelessness in REST achieves this by deploying the same API to multiple servers. Any server can handle any request, since there is no session-related dependency on the server.
Easy to design, implement, and manage: The stateless and uniform interface property helps in this, as fewer complications arise due to stateful property.
Flexible and portable: Data can be migrated between servers, and underlying databases can be changed without affecting the client’s request or response.
Client and server are independent: Due to the stateless property of REST, the developers can work independently on the client and server side.
No need for server-side synchronization logic: This makes the stateless API less complex.
Easy to cache: Clients don't need to worry about the possibility of the state from a previous request affecting the caching ability of the current request. This improves the application’s performance.
Less costly: There is no need for memory allocation and backing storage.
Best Practices for Adopting REST APIs
REST has been widely adopted as a popular architecture style for the development of APIs. Developers around the world have widely accepted certain best practices, which we’ll discuss below.
Always try to use JSON as the format for representation of resources and in sending requests as well. JSON is highly intuitive, and most languages have pre-built functions or libraries to parse and manipulate JSON objects. Many frameworks use JSON as an intermediary format to transfer data and provide converters or mappers to translate JSON into their application’s native format and back to JSON from it. Most of the popular languages such as Python, Java, C++ have internal or external libraries that can read and write JSON data.
Use Nouns Instead of Verbs in URL
Always use nouns that represent a resource of your application. These resources are business entities such as users, customers, and products. Instead of using verbs like create-post or delete-user, use nouns in endpoints and leverage HTTP methods such as
DELETE, to perform operations on the resources.
For example: To operate a basic Create, Retrieve, Update, Delete (CRUD) operation on an entity user, we can use the following endpoints and methods instead of create-user, delete-user.
Operation: Get details of all users
Operation: Get details of a user with a particular name
Operation: Create a new user
To avoid any confusion and unnecessary complexity, errors should be gracefully handled with proper HTTP return codes such as 401, 403, and 500 to indicate the kind of error that has occurred, along with a message stating the reason this error could have occurred. This allows users to better understand what went wrong with the request.
Documentation is a key aspect of any API. It is the first thing that the user sees. If it is not well compiled in a systematic way and with proper flow, clients will be discouraged from using it. The OpenAPI or Swagger are both well-known, industry-wide accepted formats for defining REST APIs. They facilitate proper documentation of REST APIs for developers.
Allow Sorting, Filtering, and Pagination
The data for a resource can be huge, resulting in clients fetching large volumes of data when only a subset of the data is required. Always allow filtering and pagination of data so that only a certain volume of data is passed on with each response. The clients can make requests for more data.
While there are other options like the trending technology of GraphQL, REST APIs are already de facto standard and dominate the API market. Their flexibility, portability, and scalability make them an ideal choice for large enterprise APIs. Amplication is one of them. Our backend development platform helps you to generate production-ready REST APIs automatically including authentication, auto generates endpoints based on best practices, pagination, sorting, filtering, error handling and more. This means you don’t end up stuck in the structural aspects of an application, enabling you to focus on functionality and performance instead.