What is backward compatibility? How have you achieved backward compatibility in your systems?

Backward compatibility is the ability of a system or component to work with older versions of data, interfaces, or protocols without breaking functionality.

To achieve backward compatibility, the following are usually applied:

• Supporting old APIs alongside new ones (API versioning)
• Not removing or changing existing data fields, but adding new ones
• Using adapters or facades to convert old formats to new ones

For example, in an API, you can add a version to the URL (/api/v1/, /api/v2/) and support both versions so that clients on older versions do not break.

In my systems, I used a gradual update strategy with support for multiple API versions and data migration while preserving old formats to avoid disrupting client operations.