Application programming interfaces (APIs) are an integral part of software development. They allow different applications to communicate with each other by calling on functions and services. APIs essentially act as a contract between various pieces of software. However, sometimes APIs need to be updated or changed in a way that breaks backwards compatibility. These are known as “breaking changes” and can cause significant headaches for developers if not handled properly.
Why are breaking API changes sometimes necessary?
There are a few key reasons why breaking API changes occur:
- New features or functionality need to be added that require changes to the API contract
- Security vulnerabilities or bugs need to be fixed
- The API needs to be optimized for performance/efficiency
- The API needs to be updated to support newer technologies or standards
While maintaining backwards compatibility is ideal, it’s not always possible when making major improvements or fixes. There comes a time when the API needs to evolve in ways that will break existing integrations. The key is managing those breaking changes responsibly.
What qualifies as a breaking change?
There are a few types of changes to an API that would be considered breaking:
- Removing or renaming an endpoint
- Changing the signature of a method or function
- Modifying the expected parameters for a method call
- Changing the expected response format
- Removing or modifying an existing data model or schema
- Changing the expected status codes for responses
Essentially any change that forces consumers of the API to modify their existing integrations would be a breaking change. If the API change means that current calls start failing unless updated, then it breaks backwards compatibility.
Examples of breaking API changes
Here are some concrete examples of changes that would break an API:
- Removing the /users endpoint for looking up user accounts
- Changing the getUser() method to expect a numeric ID instead of a username string
- Modifying the JSON response for the getOrders() endpoint to return an array instead of a single object
- Requiring an extra authToken parameter in API calls
- Changing HTTP response codes like replacing 200 OK with 400 Bad Request
Any of these changes would break existing API integrations and require updates on the consumer side before things would work again.
Best practices for breaking API changes
While breaking changes can’t always be avoided, there are some best practices companies should follow to ease the transition:
- Provide detailed changelog notes – Clearly document what changes are being made and how consumers will be affected.
- Announce changes well in advance – Give consumers time to prepare for changes, ideally 60+ days notice.
- Support legacy API versions for a period of time – Run the old and new API versions side-by-side to give consumers more flexibility in updating.
- Use semantic versioning – Breaking changes should result in incrementing the MAJOR version number according to semver principles.
- Offer migration guides – Provide instructions and tools to help consumers update their integrations.
- Introduce deprecation warnings – Return warnings for a period of time before fully removing deprecated endpoints or features.
Following API best practices helps provide a smooth transition and minimizes disruption for users.
Versioning strategies for APIs
There are a few common versioning strategies used when modifying APIs:
- URI Versioning – The API version is included in the URL itself (e.g. http://api.example.com/v1/users)
- Request Parameter Versioning – The API version is passed in as a parameter like ?version=1.2
- Header Versioning – Custom HTTP headers specify the version (e.g. Api-Version: 1.1)
- Media Type Versioning – Uses Accept and Content-Type headers to version media types (e.g. application/vnd.example.v1+json)
Each approach has pros and cons. URI versioning is very explicit and permanent but can lead to API sprawl over time. Parameter or header based versioning keeps URIs clean but headers can get lost. Media type versioning allows content negotiation but Accept headers can get long.
Often a combination of techniques is most optimal. Use URI versioning for major versions and headers for minor versions for example. The key is finding an approach that balances developer experience and long-term API maintenance.
Deprecating APIs safely
Removing old APIs or features requires carefully handling deprecation:
- Announce deprecation schedule – Share timelines for when endpoints will be deprecated and eventually removed.
- Return warnings in responses – Include messages indicating deprecation and alternative options.
- Monitor usage – Track usage of deprecated features to gauge impact of removal.
- Enforce sunsetting – Eventually cut off access to deprecated versions per schedule.
- Suggest replacements – Provide code samples and docs to redirect users to supported alternatives.
Following a clear deprecation policy ensures developers have time to safely update their integrations without disruption. Make the transition easy by offering plenty of warnings, documentation, and replacement options.
Tools for managing API changes
API management platforms and developer portals can help streamline breaking API changes:
- API documentation – Catalog all API changes in associated docs and changelogs.
- Developer communication – Email, notify, or alert developers of impactful API updates.
- Versioning control – Apply tags and release processes to API changes.
- Deprecation management – Set schedules and provide warnings for deprecated APIs.
- Analytics – Monitor API usage to gauge the impact of changes.
Centralized API management makes it easier for both API providers and consumers to deal with the complexity of continuous API evolution.
Testing strategies for API changes
Rigorously testing API changes helps avoid unintended side effects:
- Sandbox testing – Test changes in a sandbox environment before deploying to production.
- Automated regression testing – Use automated tests to detect API bugs and failures.
- Consumer driver testing – Test changes via the consumer’s perspective with their own apps/clients.
- Beta testing programs – Release changes to a small group of testers before general availability.
- Monitor health metrics – Check API uptime, throughput, and error rates for anomalies.
Continuous testing is crucial to ensure breaking API changes do not also break downstream applications relying on the API. Test both the provider and consumer angles.
Conclusion
Breaking API changes are often necessary to add new capabilities and maintain healthy API lifecycles. But they require careful planning and communication to avoid negatively impacting consumers. Follow best practices around versioning, deprecation, tooling, and testing when introducing breaking API changes. Emphasize clear documentation, reasonable timelines, and migration guidance for a smooth transition.