Backward-Compatible Change

Overview

Backward-Compatible Change is a modification that allows existing conforming clients to continue operating without mandatory code or configuration changes. It describes a particular change, while backward compatibility describes the broader property maintained across versions.

The principal risks include clients using strict parsers, changed defaults, new enum values, altered validation, performance regressions, undocumented semantic changes, and dependencies that interpret optional data differently. Operational metrics for Backward-Compatible Change should use stable denominators and separate technical activity from successful business completion.

A production implementation should follow the published contract, add rather than repurpose fields, keep existing meanings stable, make new inputs optional, tolerate unknown response fields, and test representative old clients. The Backward-Compatible Change runbook should define who can retry, cancel, replay, reconcile, communicate, and approve an exception.

Useful measures include old-client success rate, schema-compatibility test results, version adoption, regression incidents, deprecation exceptions, and support cases after release. Backward-Compatible Change is closely connected to Backward Compatibility, OpenAPI Document, and Response Schema. The production boundary for Backward-Compatible Change should identify the authoritative system, responsible owner, accepted states, and recovery path.

For Backward-Compatible Change, identifiers and timestamps should remain stable enough to trace the technical action to its final business outcome. Monitoring for Backward-Compatible Change should distinguish transport success, processing success, and the final external or financial result.

Changes to Backward-Compatible Change should be tested against normal, failed, delayed, duplicate, and recovery paths that apply to the operation. Evidence for Backward-Compatible Change should preserve the input, configuration version, actor or service, decision, downstream reference, and final outcome.