Amazon ECS Event Stream for CloudWatch Events
You can use Amazon ECS event stream for CloudWatch Events to receive near real-time notifications regarding the current state of both the container instances within an Amazon ECS cluster, and the current state of all tasks running on those container instances.
Using CloudWatch Events, you can build custom schedulers on top of Amazon ECS that are responsible for orchestrating tasks across clusters, and to monitor the state of clusters in near real time. With Amazon ECS CloudWatch events, you can eliminate scheduling and monitoring code that continuously polls the Amazon ECS service for status changes, and instead handle Amazon ECS state changes asynchronously using any CloudWatch Events target, such as AWS Lambda, Amazon Simple Queue Service, Amazon Simple Notification Service, and Amazon Kinesis Streams.
Events from Amazon ECS Event Stream are ensured to be delivered at least one time. In the event that duplicate events are sent, the event provides enough information to identify duplicates. For more information, see Handling Events
Events are relatively ordered, so that you can easily tell when an event occurred in relation to other events.