How can you manage versioning in SOAP and REST?

1 SOAP Versioning

SOAP, or Simple Object Access Protocol, is a protocol based on XML that defines a standard way of exchanging messages between web services. SOAP uses a contract-first approach, meaning that you have to define the structure and semantics of your messages in a WSDL (Web Services Description Language) document. This document acts as a contract between the service provider and the consumers, and specifies the operations, parameters, and responses that the service supports. To manage versioning in SOAP, you have to modify the WSDL document and update the consumers accordingly. There are two main strategies for SOAP versioning: backward compatible and backward incompatible.

Backward compatible versioning means that you can add new features or modify existing ones without affecting the existing functionality or breaking the contract. For example, you can add new optional parameters, elements, or attributes, or change the order of elements, as long as you do not remove or rename any existing ones. This way, the old consumers can still use the service without any changes, while the new consumers can benefit from the new features. However, this strategy can also lead to complexity and bloat in the WSDL document, as you have to maintain all the previous versions and avoid conflicts.

Backward incompatible versioning means that you have to change the contract in a way that affects the existing functionality or breaks the compatibility with the old consumers. For example, you can remove or rename existing parameters, elements, or attributes, or change the data types or namespaces. This way, you can simplify and optimize the WSDL document, and introduce major changes or improvements. However, this strategy also requires that you notify and update all the consumers, and provide them with a new version of the WSDL document. You can also use different endpoints or URIs for different versions of the service, to avoid confusion and errors.

2 REST Versioning

REST, or Representational State Transfer, is an architectural style that defines a set of principles and constraints for designing web services that are based on the HTTP protocol and the concept of resources. REST uses a code-first approach, meaning that you do not have to define a contract or a schema for your messages, but rather rely on the HTTP methods, headers, and status codes to communicate with the service. To manage versioning in REST, you have to decide how to indicate the version of the service and how to handle the changes and updates. There are three main strategies for REST versioning: URI, header, and media type.

URI versioning means that you include the version number in the URI of the service, either as a path parameter or a query parameter. For example, you can use /api/v1/users or /api/users?version=1 to access the first version of the service. This way, you can easily identify and access different versions of the service, and provide a clear and consistent way for the consumers to request the version they want. However, this strategy can also violate the REST principles of uniform interface and resource identification, as it implies that the same resource can have different URIs depending on the version.

Header versioning means that you use a custom HTTP header to specify the version of the service, either as a request or a response header. For example, you can use X-API-Version: 1 or Accept-Version: 1 to request the first version of the service. This way, you can keep the URI of the service clean and consistent, and adhere to the REST principles of uniform interface and resource identification. However, this strategy can also be less visible and discoverable, as it requires the consumers to know and use the custom header, and the documentation to explain the header usage and values.

Media type versioning means that you use the standard HTTP header of Content-Type or Accept to indicate the version of the service, by using a custom media type that includes the version number. For example, you can use application/vnd.myapi.v1+json or application/vnd.myapi+json;version=1 to request the first version of the service. This way, you can leverage the existing HTTP mechanism of content negotiation, and express the version as part of the representation format of the resource. However, this strategy can also be complex and cumbersome, as it requires you to define and register custom media types, and handle the parsing and validation of the media type parameters.