Which deployment model allows for instant rollback to a previous version in Google Kubernetes Engine (GKE)?

The blue/green deployment model is designed to enable instant rollback to a previous version with minimal downtime. In this model, two identical environments—one 'blue' (the current version) and one 'green' (the new version)—are created. When the green environment is ready, traffic is switched from blue to green. If any issues arise with the new version, switching back to the blue environment can be done almost instantaneously. This provides a highly reliable mechanism for rolling back changes.

In contrast, other deployment approaches, while beneficial in their own rights, do not inherently facilitate such swift rollbacks. Rolling deployments update a portion of instances incrementally, which can complicate the rollback process as it might involve reverting multiple changes across various instances. A/B testing focuses on evaluating multiple versions to determine which performs better, thus it is not aimed at seamless rollbacks. Canary deployments gradually shift traffic to the new version, but if issues are detected, while it's possible to revert, it usually requires more manual intervention than the instant switch provided by blue/green deployments.