In the landscape of web services, two major communication protocols have been at the forefront: Simple Object Access Protocol (SOAP) and Representational State Transfer (REST). Over the years, REST has increasingly become the de facto standard for the development of web services, edging out SOAP in many use cases. This shift wasn’t accidental; it resulted from REST’s simplicity, flexibility, and alignment with web technologies. In this post, we’ll explore the reasons why REST supplanted SOAP as the protocol of choice for cross-application communication.

A Brief History: SOAP vs. REST

SOAP, developed by Microsoft in the late 1990s, was designed to enable programs running on different operating systems to communicate using the Internet. It uses XML for its message format and relies heavily on other standards to ensure security, transactions, and messaging patterns. SOAP was widely adopted for enterprise-level web services that required complex transactions and high security.

SOAP Request:

POST /BookService HTTP/1.1
Host: example.com
Content-Type: text/xml; charset=utf-8
Content-Length: length

<?xml version="1.0"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"
               xmlns:lib="http://example.com/library">
    <soap:Body>
        <lib:AddBookRequest>
            <lib:title>New Book Title</lib:title>
            <lib:author>Author Name</lib:author>
            <lib:year>2021</lib:year>
        </lib:AddBookRequest>
    </soap:Body>
</soap:Envelope>

SOAP Response:

HTTP/1.1 200 OK
Content-Type: text/xml; charset=utf-8
Content-Length: length

<?xml version="1.0"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"
               xmlns:lib="http://example.com/library">
    <soap:Body>
        <lib:AddBookResponse>
            <lib:result>Success</lib:result>
            <lib:bookId>123</lib:bookId>
        </lib:AddBookResponse>
    </soap:Body>
</soap:Envelope>

In this SOAP example, the action (adding a new book) is specified within the XML payload, encapsulated in a AddBookRequest element. The SOAP envelope (soap:Envelope) wraps the request, which includes the details of the book to be added (title, author, year). The server processes this request and returns a response wrapped in a similar SOAP envelope, indicating the result of the operation and, if successful, providing the ID (bookId) of the newly added book.

REST, on the other hand, was introduced by Roy Fielding in his 2000 doctoral dissertation. It’s not a protocol or standard but an architectural style for distributed systems. RESTful web services use HTTP requests to post data (create and/or update), read data (e.g., make queries), and delete data, thus treating web service endpoints as resources and using URL structures to represent them. This simplicity and adherence to the existing architecture of the web made REST a compelling alternative to SOAP.

REST Request:

POST /books HTTP/1.1
Host: example.com
Content-Type: application/json
Content-Length: length

{
  "title": "New Book Title",
  "author": "Author Name",
  "year": 2021
}

In a RESTful service, the action to add a new book is represented as a POST request to the /books endpoint. The request body, formatted as JSON, contains the new book’s details, including the title, author, and year.

REST Response:

HTTP/1.1 201 Created
Content-Type: application/json
Content-Length: length

{
  "result": "Success",
  "bookId": 123,
  "title": "New Book Title",
  "author": "Author Name",
  "year": 2021
}

Upon successful creation, the server responds with a status code of 201 (Created), along with a JSON representation of the newly added book, including a generated bookId that uniquely identifies this resource in the library’s collection.

To access this book entry later, simply issue the following request:

REST Request:

GET /books/123 HTTP/1.1
Host: example.com

This GET request is made to the /books/123 endpoint, where 123 is the ID of the book we want to retrieve. The use of the GET method signifies that we are requesting data for a specific book and not modifying any resources.

REST Response:

HTTP/1.1 200 OK
Content-Type: application/json
Content-Length: length

{
  "bookId": 123,
  "title": "New Book Title",
  "author": "Author Name",
  "year": 2021
}

AJAX (Asynchronous JavaScript and XML) was also a pivotal force in the ascendancy of REST APIs by enabling web applications to communicate with a server asynchronously, thereby creating more dynamic, responsive, and interactive user experiences. This shift towards more agile web applications necessitated lightweight and stateless communication mechanisms, qualities inherent to RESTful services, which could efficiently handle data in formats like JSON, making REST APIs the preferred choice for developers aiming to leverage AJAX’s full potential in modern web development.

Simplicity and Flexibility

One of the key reasons REST gained popularity over SOAP is its simplicity. REST uses the HTTP protocol for communication, making it easier to implement and understand. Developers can use standard HTTP methods such as GET, POST, PUT, and DELETE to perform operations on resources. This simplicity accelerates development and reduces the learning curve, making REST an attractive option for web developers.

Additionally, REST does not enforce a strict message format like SOAP, which relies on XML. Instead, RESTful services can return data in various formats, including JSON, XML, YAML, plain text, or even binary formats like protobuf, msgpack, and bson, depending on the client’s needs. This flexibility allows RESTful services to be more lightweight and faster than SOAP, especially beneficial when bandwidth is a concern, such as in mobile applications or services targeting emerging markets with limited internet connectivity.

Alignment with Web Technologies

REST’s design philosophy is closely aligned with the stateless nature of the web, leveraging the ubiquitous HTTP protocol. This alignment with web technologies means that RESTful services can be easily consumed by any client that understands HTTP, without the need for specialized software or libraries required by SOAP. This universality has led to wider adoption of REST in web development, where developers seek out technolgies that are easier to use, work across platforms, and have a widely shared knowledge base.

Furthermore, the popularity of web APIs has exploded in the era of web 2.0 and beyond, with companies and services providing access to their functionalities via RESTful interfaces. This ecosystem has fostered a community of developers familiar with REST principles, further cementing its dominance.

Better Performance and Scalability

RESTful services typically offer better performance and scalability compared to SOAP. This is primarily due to the lightweight nature of REST, which uses less bandwidth and resources. SOAP messages are often larger because of the verbosity of XML, and the overhead of processing SOAP messages can lead to slower response times.

Moreover, REST’s stateless operations align well with the scalable architecture of the web, allowing RESTful services to handle high volumes of requests efficiently. This scalability is crucial for modern applications and services that need to serve a growing number of users with minimal latency.

Wider Community Support and Tooling

As REST has grown in popularity, so has the ecosystem around it, including tools, libraries, and community support. Frameworks like Express for Node.js, Django Rest Framework for Python, and Spring Boot for Java make it easy to develop RESTful services. These frameworks offer features like automatic routing, request and response handling, and serialization, reducing the amount of boilerplate code developers need to write.

The widespread adoption of REST has also led to a wealth of community resources, tutorials, and documentation available to help developers troubleshoot issues and implement best practices. This supportive ecosystem is invaluable for developers new to REST or looking to leverage its full potential.

Transition to Microservices and Beyond

The evolution of architectural styles, particularly the move towards microservices, has further reinforced REST’s position. Microservices architectures break down applications into small, loosely coupled services that communicate over lightweight protocols like HTTP. REST’s stateless communication model fits naturally with microservices, enabling individual services to be developed, deployed, and scaled independently.

Conclusion

The transition from SOAP to REST as the preferred protocol for cross-application communication is a testament to REST’s simplicity, flexibility, and performance. While SOAP still has its place in scenarios that require strict transactional reliability and security, REST’s advantages align more closely with the needs of modern web development. By embracing HTTP and leveraging web technologies, RESTful services offer an efficient, scalable, and easy-to-use alternative that has reshaped how developers approach web service design. As technology continues to evolve, REST’s principles of simplicity and efficiency will likely continue to influence the development of web services and beyond.

Beyond REST, several new technologies are showing promise: GraphQL and gRPC. It will be interesting to see if either of these will provide the next stepping stone of the Web’s evolution.