Track Amazon ECS Availability Zone rebalancing

You can verify if Availability Zone rebalancing is enabled for a service in the console or by calling describe-services. The following example can be used to see the status with the CLI.

The response will be either ENABLED or DISABLED.

aws ecs describe-services \
    --services service-name \
    --cluster cluster-name \
    --query services[0].availabilityZoneRebalancing

Service events

Amazon ECS sends service action events to help you understand the Availability Zone rebalancing lifecycle.

Event	Scenario	Type	Learn more
SERVICE_REBALANCING_STARTED	Amazon ECS starts an Availability Zone rebalancing operation	INFO	service (service-name) is not AZ balanced with number-tasks tasks in Availability Zone 1, number-tasks in Availability Zone 2, and number-tasks in Availability Zone 3. AZ Rebalancing in progress.
SERVICE_REBALANCING_COMPLETED	The Availability Zone rebalancing operation completes	INFO	service (service-name) is AZ balanced with number-tasks tasks in Availability Zone 1, number-tasks tasks in Availability Zone 2, and number-tasks tasks in Availability Zone 3.
TASKS_STARTED	Amazon ECS successfully start tasks as part of the Availability Zone rebalancing operation	INFO	service-name has started number-tasks tasks in Availability Zone to AZ Rebalance: task-ids.
TASKS_STOPPED	Amazon ECS successfully stops tasks as part of the Availability Zone rebalancing operation	INFO	service-name has stopped number-tasks running tasks in Availability Zone due to AZ rebalancing: task-id.
SERVICE_TASK_PLACEMENT_FAILURE	Amazon ECS failed to start a task as part of the Availability Zone rebalancing operation	ERROR	For the EC2 launch type, see service (service-name) is unable to place a task in Availability Zone because no container instance met all of its requirements. For the Fargate launch type, see service (service-name) is unable to place a task in Availability Zone.
TASKSET_SCALE_IN_FAILURE_BY_TASK_PROTECTION	The Availability Zone rebalancing operation is blocked because task protection is in use.	INFO	service (service-name) was unable to AZ Rebalance because task-set-name was unable to scale in due to reason.
SERVICE_REBALANCING_STOPPED	The Availability Zone rebalancing operation stopped. Amazon ECS sends additional events which provide more information.	INFO	service (service-name) stopped AZ Rebalancing.

Task state change events

Amazon ECS sends a task state change event (START) for each task that is starts as part of the rebalancing process.

Amazon ECS sends a task state change event (STOPPED) event for each task that it stops as part of the rebalancing process. The reason is set to Availability Zone rebalancing initiated by (deployment ecs-svc/deployment-id).

For more information about the events, see Amazon ECS task state change events.