In today's fast-paced and interconnected world, Application Programming Interfaces (APIs) play a crucial role in enabling seamless communication and integration between different systems and applications. With the increasing adoption of APIs, there is a growing need for organizations to effectively manage the entire lifecycle of their APIs, from design to release. This article explores the key aspects of API lifecycle management, providing insights into how a shared model and vocabulary can simplify governance, enhance productivity, and provide practical guidance for developers.

The API lifecycle consists of several distinct phases, each playing a vital role in ensuring the successful development and deployment of APIs. These phases include:

• Discovery: The initial phase, outside of the API lifecycle, focuses on demand generation, prioritization, and planning. It involves identifying the need for an API and creating a prioritized backlog that will guide the subsequent phases.
• Evolution: This phase involves observation, evaluation, and client feedback on APIs deployed in test or production environments. Any necessary design changes, whether breaking or non-breaking, are made based on this feedback.
• Design: The design phase starts with developing a model of the domain through stakeholder consultation and frequent iterations. A collaborative, version-controlled domain data modeling tool is recommended to ensure the accuracy and accessibility of the domain model. This model acts as a ubiquitous language, facilitating communication between developers and domain experts.
• Build & Test: In this phase, the API implementation is built according to design and security standards. The prototype OpenAPI document and JSON schema generated from the domain model serve as inputs for the build process. The API is deployed to sandbox and development environments for iteration and testing, possibly using a mock service. Continuous integration, automation, and testing practices ensure that the API meets all functional and security requirements.
• Evaluate: During the evaluation phase, thorough testing, client engagement, and analytics provide valuable insights into the performance and functionality of the API. This evaluation process may result in either promoting the API for release or necessitating further rework and refinement.

API lifecycle states play a crucial role in determining the stability and support level of an API. The following states are commonly observed in the API lifecycle:

• In Design: APIs in the design phase are subject to change at any time, and feedback is encouraged. This phase allows for flexibility and iteration, ensuring that the API design aligns with user needs and requirements.
• In Test: APIs in the testing phase continue to gather feedback, with the possibility of making breaking changes based on the evaluation results. This phase focuses on ensuring the robustness and reliability of the API before its release.
• Published: APIs that have successfully completed the testing phase and met all requirements are released to production. These APIs are considered stable, actively supported, and suitable for consumption by consumers.
• Deprecated: When a new version of an API is released, the previous version enters the deprecated state. While existing consumers can continue using the deprecated API, new clients are unable to subscribe. API owners maintain support for the deprecated API for a specific period, allowing time for existing clients to transition to the new version.
• Retired: Once all existing clients have transitioned to the new version, or when the scheduled retirement date arrives, the API is retired. Calls to the retired API will result in a gateway error, reflecting the discontinuation of support and availability.

Maintaining stability while allowing for continuous improvement is a critical challenge in API lifecycle management. Organizations often need to support more than one version of an API to avoid disruption and facilitate a coordinated transition. Here are some key considerations for managing API versions:

• Versioning APIs: Versioned URLs, such as api.example.com/v1/resource, are widely used to manage API versions. This simple and intuitive approach allows clients to control which versions they interact with. Semantic versioning (MAJOR.MINOR.PATCH) is recommended for managing API models and specifications, ensuring clarity and coherence in versioning.
• Backwards Compatibility: Backwards compatible changes are crucial for maintaining interoperability between different API versions. Addition of new fields, operations, HATEOAS links, or media type support are considered backwards compatible. However, removal or changes of fields, operations, or media type support are not considered backwards compatible.
• Replacing Major API Versions: Introducing a new major version of an API requires careful consideration and documentation. API owners should explore alternatives and determine the potential impacts before deciding on a major version change. Implementing a new major version should involve decoupling the cut-over, communicating a retirement schedule for the previous version, and eventually retiring the old version once all clients have transitioned.

Security is a critical aspect of API lifecycle management, and it should be embedded into each phase to ensure the protection of data and prevent vulnerabilities. Here are key aspects of security integration throughout the API lifecycle:

• Data Classification: During the modeling phase, data should be classified, and regulatory controls should be identified to ensure compliant handling of sensitive information.
• API Development Guidelines: Developers should adhere to API development guidelines that outline best practices and tactics for securing APIs, mitigating common security risks.
• API Specification Linting: API specifications should be linted during integration into source control to identify and address any security-related issues or inconsistencies.
• API Gateway Security: API management platforms and gateways enforce security policies, applying security measures to protect the API and its consumers.
• OWASP Testing: APIs should undergo thorough security testing, including OWASP testing, to identify and address potential vulnerabilities.

API lifecycle management is a crucial aspect of modern software development, enabling organizations to effectively design, build, and maintain APIs. A shared API lifecycle model and vocabulary provide a foundation for streamlining governance, boosting productivity, and guiding developers in every step of the API development process. By embracing this comprehensive approach to API lifecycle management, organizations can ensure the stability, security, and success of their API initiatives.