Container Instance Draining
There are times when you might need to remove an instance from a cluster; for example, to perform system updates, update the Docker daemon, or scale down the cluster size. Container instance draining enables you to remove a container instance from a cluster without impacting tasks in your cluster.
When you set a container instance to
DRAINING, Amazon ECS prevents new tasks
from being scheduled for placement on the container instance. If the resources are
available, replacement service tasks are started on other container instances in the
cluster. Service tasks on the container instance that are in the
state are stopped immediately.
Service tasks on the container instance that are in the
RUNNING state are
stopped and replaced according to the service's deployment configuration parameters,
minimumHealthyPercentis below 100%, the scheduler can ignore
desiredCounttemporarily during task replacement. For example,
desiredCountis four tasks, a minimum of 50% allows the scheduler to stop two existing tasks before starting two new tasks. If the minimum is 100%, the service scheduler can't remove existing tasks until the replacement tasks are considered healthy. If tasks for services that do not use a load balancer are in the
RUNNINGstate, they are considered healthy. Tasks for services that use a load balancer are considered healthy if they are in the
RUNNINGstate and the container instance they are hosted on is reported as healthy by the load balancer.
maximumPercentparameter represents an upper limit on the number of running tasks during task replacement, which enables you to define the replacement batch size. For example, if
desiredCountof four tasks, a maximum of 200% starts four new tasks before stopping the four tasks to be drained (provided that the cluster resources required to do this are available). If the maximum is 100%, then replacement tasks can't start until the draining tasks have stopped.
RUNNING tasks that do not belong to a service
are unaffected; you must wait for them to finish or stop them manually.
A container instance has completed draining when there are no more
RUNNING tasks (although the state remains as
You can verify this using the ListTasks operation with the
When you change the status of a container instance from
ACTIVE, the Amazon ECS scheduler can schedule tasks on the instance
The following procedure demonstrates how to set your instance to
DRAINING using the AWS Management Console.
To set your instance to
DRAINING using the console
Open the Amazon ECS console at https://console.aws.amazon.com/ecs/.
In the navigation pane, choose Clusters and select the cluster.
Choose ECS Instances and select the check box for the container instances.
Choose Actions, Drain instances.
After the instances are processed, choose Done.