AWS Lambda versions and aliases are designed specifically to support safe deployments, testing, and rollback. A Lambda version is immutable, meaning its code and configuration cannot change once published. Aliases act as pointers to specific versions and can be updated instantly.

AWS documentation recommends using aliases to manage environments such as dev , test , and prod . Each environment can reference a specific Lambda version, allowing the same function codebase to be promoted across accounts with confidence. If a defect is detected in production, the alias can be quickly repointed to a previously known good version, enabling an immediate rollback without redeployment.

Options B, C, and D introduce higher operational overhead or do not provide safe rollback. Deploying separately increases risk and management effort. Lambda layers are not intended for environment promotion. Environment variables do not protect against faulty code deployments.

Therefore, using Lambda versions and aliases is the most efficient and AWS-recommended solution.