# Create a step scaling policy for Amazon ECS service auto scaling
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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
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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](auto-scaling-IAM.md).

1. 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.

1. Create the CloudWatch alarms for the metrics. For more information, see [Create a CloudWatch alarm based on a static threshold](https://docs.amazonaws.cn/AmazonCloudWatch/latest/monitoring/ConsoleAlarms.html) in the *Amazon CloudWatch User Guide*.

1. Open the console at [https://console.amazonaws.cn/ecs/v2](https://console.amazonaws.cn/ecs/v2).

1. On the **Clusters** page, choose the cluster.

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

   The service details page appears.

1. Choose **Set the number of tasks**.

1. 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.

   1. 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.

   1. Choose **Save**.

      The policies page appears.

1. Choose **Create scaling policy**.

   The **Create policy** page appears.

1. For **Scaling policy type**, choose **Step Scaling**.

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

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

   1. For **CloudWatch alarm name**, choose the CloudWatch alarm.

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

   1. For A**djustment types**, choose whether the adjustment is based on a change in the number of tasks, or a change in the percentage of tasks.

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

      Choose **Add step** to add additional actions.

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

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

   1. For **CloudWatch alarm name**, choose the CloudWatch alarm.

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

   1. 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.

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

      Choose **Add step** to add additional actions.

1. 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. 

1. Choose **Create scaling policy**.

## Amazon CLI
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1. Register your Amazon ECS service as a scalable target using the [register-scalable-target](https://docs.amazonaws.cn/cli/latest/reference/application-autoscaling/register-scalable-target.html) command.

1. Create a scaling policy using the [put-scaling-policy](https://docs.amazonaws.cn/cli/latest/reference/application-autoscaling/put-scaling-policy.html) command.