A migration team needs a reversible cutover from an old API to a new implementation. Both versions can serve the same contract, and traffic must increase gradually only while metrics remain healthy. Which design fits?

1. Use a supported canary routing mechanism with health criteria and a tested rollback path.
2. Move all traffic immediately and remove the old implementation before validation.
3. Change the DNS record once and assume existing connections instantly obey the new setting.
4. Compare only deployment package sizes as the release health signal.