minimumHealthyPercent

If a service is using the rolling update (ECS) deployment type, the minimumHealthyPercent represents a lower limit on the number of your service's tasks that must remain in the RUNNING state during a deployment, as a percentage of the desiredCount (rounded up to the nearest integer). This parameter enables you to deploy without using additional cluster capacity. For example, if your service has a desiredCount of four tasks and a minimumHealthyPercent of 50%, the service scheduler may stop two existing tasks to free up cluster capacity before starting two new tasks.

If any tasks are unhealthy and if maximumPercent doesn't allow the Amazon ECS scheduler to start replacement tasks, the scheduler stops the unhealthy tasks one-by-one — using the minimumHealthyPercent as a constraint — to clear up capacity to launch replacement tasks. For more information about how the scheduler replaces unhealthy tasks, see Amazon ECS services .

For services that do not use a load balancer, the following should be noted:

• A service is considered healthy if all essential containers within the tasks in the service pass their health checks.

• If a task has no essential containers with a health check defined, the service scheduler will wait for 40 seconds after a task reaches a RUNNING state before the task is counted towards the minimum healthy percent total.

• If a task has one or more essential containers with a health check defined, the service scheduler will wait for the task to reach a healthy status before counting it towards the minimum healthy percent total. A task is considered healthy when all essential containers within the task have passed their health checks. The amount of time the service scheduler can wait for is determined by the container health check settings.

For services that do use a load balancer, the following should be noted:

• If a task has no essential containers with a health check defined, the service scheduler will wait for the load balancer target group health check to return a healthy status before counting the task towards the minimum healthy percent total.

• If a task has an essential container with a health check defined, the service scheduler will wait for both the task to reach a healthy status and the load balancer target group health check to return a healthy status before counting the task towards the minimum healthy percent total.

The default value for a replica service for minimumHealthyPercent is 100%. The default minimumHealthyPercent value for a service using the DAEMON service schedule is 0% for the CLI, the Amazon Web Services SDKs, and the APIs and 50% for the Amazon Web Services Management Console.

The minimum number of healthy tasks during a deployment is the desiredCount multiplied by the minimumHealthyPercent/100, rounded up to the nearest integer value.

If a service is using either the blue/green (CODE_DEPLOY) or EXTERNAL deployment types and is running tasks that use the EC2 launch type, the minimum healthy percent value is set to the default value. The minimum healthy percent value is used to define the lower limit on the number of the tasks in the service that remain in the RUNNING state while the container instances are in the DRAINING state.

You can't specify a custom minimumHealthyPercent value for a service that uses either the blue/green (CODE_DEPLOY) or EXTERNAL deployment types and has tasks that use the EC2 launch type.

If a service is using either the blue/green (CODE_DEPLOY) or EXTERNAL deployment types and is running tasks that use the Fargate launch type, the minimum healthy percent value is not used, although it is returned when describing your service.