Which deployment approach allows instant rollback if issues occur?

Blue/green deployment is a release strategy that minimizes downtime and risk by running two identical production environments, referred to as "Blue" and "Green." Only one environment is live at any time. To deploy a new version, you deploy it to the inactive environment (e.g., Green) while the current version runs on the live one (Blue). After testing the Green environment, you switch the router to direct all incoming traffic to it. If any issues arise with the new version, you can perform an instant rollback by simply switching the router back to the Blue environment, which is still running the previous stable version.

B. Canary: This involves a gradual rollout to a subset of users. Rollback is possible but is not an instant, single-action switch like in blue/green.

C. Shadow: This strategy runs a new version alongside the old one without serving its responses to users, primarily for testing and not for live deployment with instant rollback.

D. Batch: This is a method for processing data for inference and is not a deployment strategy for online endpoints that facilitates rollback.

1. Microsoft. (2023). Safe rollout for online endpoints. Microsoft Learn. Retrieved from https://learn.microsoft.com/en-us/azure/machine-learning/how-to-safely-rollout-online-endpoints. (Under the "Blue-green deployment" section, it states: "If there's an issue, you can revert to the previous version... by switching traffic back to the blue deployment.")

2. Fowler, M. (2010). BlueGreenDeployment. MartinFowler.com. Retrieved from https://martinfowler.com/bliki/BlueGreenDeployment.html. (This is a foundational article from a reputable source in software engineering that defines the pattern and highlights the ability to "rapidly roll back if anything goes wrong.")