Create a step scaling policy for Amazon ECS service auto scaling

Create a step scaling policy to have Amazon ECS increase or decrease the desired number of tasks in your service automatically. Step scaling runs based on a set of scaling adjustments, known as step adjustments, that vary based on the size of the alarm breach.

Console

1. In addition to the standard IAM permissions for creating and updating services, you need additional permissions. For more information, see IAM permissions required for Amazon ECS service auto scaling.

2. Determine the metrics to use for the policy. The following metrics are available:

   • ECSServiceAverageCPUUtilization – The average CPU utilization the service should use.

   • ECSServiceAverageMemoryUtilization – Average memory utilization the service should use.

   • ALBRequestCountPerTarget – The average number of requests per minute that task should ideally receive.

3. Create the CloudWatch alarms for the metrics. For more information, see Create a CloudWatch alarm based on a static threshold in the Amazon CloudWatch User Guide.

4. Open the console at https://console.aws.amazon.com/ecs/v2.

5. On the Clusters page, choose the cluster.

6. On the cluster details page, in the Services section, and then choose the service.

   The service details page appears.

7. Choose Set the number of tasks.

8. Under Amazon ECS service task count, choose Use auto scaling.

   The Task count section appears.

   1. For Minimum number of tasks, enter the lower limit of the number of tasks for service auto scaling to use. The desired count will not go below this count.

   2. For Maximum, enter the upper limit of the number of tasks for service auto scaling to use. The desired count will not go above this count.

   3. Choose Save.

      The policies page appears.

9. Choose Create scaling policy.

   The Create policy page appears.

10. For Scaling policy type, choose Step Scaling.

11. Configure the scaling-out properties. Under Steps to add tasks do the following:

    1. For Policy name, enter the name of the policy.

    2. For CloudWatch alarm name, choose the CloudWatch alarm.

    3. For Metric aggregation type, choose how to compare the selected metric to the defined threshold.

    4. For Adjustment types, choose whether the adjustment is based on a change in the number of tasks, or a change in the percentage of tasks.

    5. For Actions to take, enter the values for what action to take.

       Choose Add step to add additional actions.

12. Configure the scaling-in properties. Under Steps to remove tasks, do the following:

    1. For Policy name, enter the name of the policy.

    2. For CloudWatch alarm name, choose the CloudWatch alarm.

    3. For Metric aggregation type, choose how to compare the selected metric to the defined threshold.

    4. For Adjustment types, choose whether the adjustment is based on a change in the number of tasks, or a change in the percentage of tasks.

    5. For Actions to take, enter the values for what action to take.

       Choose Add step to add additional actions.

13. For Cooldown period, enter the amount of time, in seconds, to wait for a previous scaling activity to take effect. For an add policy, this is the time after a scale-out activity that the scaling policy blocks scale-in activities and limits how many tasks can be scale out at a time. For a remove policy, this is the time after a scale-in activity that must pass before another scale-in activity can start.

14. Choose Create scaling policy.

AWS CLI

1. Register your Amazon ECS service as a scalable target using the register-scalable-target command.

2. Create a scaling policy using the put-scaling-policy command.