What Actually Happens During an ECS Rolling Deployment

🫧 Open on Bubbles You push a new image, update an ECS service, and the console says Deployment in progress . Then it sits there. A new task appears in PENDING . It changes to RUNNING , but the old task does not go away. A minute later the old one starts draining. Eventually it disappears and the service returns to steady state. If you only watch the task count, the whole thing looks oddly slow and a little random. It is neither. Four systems are working on the deployment at the same time: The ECS scheduler