Amazon ECS improves Service Availability during Rolling deployments

Amazon Elastic Container Service (Amazon ECS) now includes enhancements that improve service availability during rolling deployments. These enhancements help maintain availability when new application version tasks are failing, when current tasks are unexpectedly terminated, or when scale-out is triggered during deployments.

Previously, when tasks in your currently running version became unhealthy or were terminated during a rolling deployment, ECS would attempt to replace them with the new version to prioritize deployment progress. If the new version could not launch successfully—such as when new tasks fail health checks or fail to start—these replacements would fail and your service availability could drop. ECS now replaces unhealthy or terminated tasks using the same service revision they belong to. Unhealthy tasks in your currently running version are replaced with healthy tasks from that same version, independent of the new version's status. Additionally, when Application Auto Scaling triggers during a rolling deployment, ECS applies scale-out to both service revisions, ensuring your currently running version can handle increased load even if the new version is failing.

These improvements respect your service's maximumPercent and minimumHealthyPercent settings. These enhancements are enabled by default for all services using the rolling deployment strategy and are available in all AWS Regions. To learn more about rolling-update deployments, refer Link.