A developer updates an AWS Lambda function that an Amazon API Gateway API uses.

To test an updated Lambda integration without impacting production traffic, the key is to isolate test requests from the production stage that real users call. In API Gateway, a stage represents a deployed snapshot of an API configuration, and each stage has its own invoke URL . Creating a separate test stage provides immediate traffic isolation because production users continue using the production stage URL, while the developer tests using the test stage URL.

Using stage variables is a common API Gateway pattern to parameterize integrations per stage. For Lambda backends, stage variables can reference different Lambda function ARNs, aliases, or versions (depending on the integration style), allowing the same API resources and methods to route to different backends per stage. This lets the developer deploy and validate the updated Lambda function only in the test stage while keeping the production stage pointing to the stable Lambda version. The result is operationally efficient: minimal duplicated infrastructure, clear separation, and easy rollback by switching stage variables or redeploying only the stage configuration.

Option A (canary on the existing stage) intentionally shifts a percentage of production traffic to the new version, which violates the requirement that testing must not affect any production users. Option B (private endpoint) changes network accessibility and can break production access; it also does not provide safe version testing. Option D (clone entire stack) can work but has higher operational overhead (duplicate resources, additional deployment management) than using native stage isolation.

Therefore, C best meets the requirements: create a new test stage , use stage variables to point that stage to the updated Lambda function, and test safely using the test stage URL while production remains unaffected.