Step 1: (Optional) Analyze time series data Step 2: Create two scheduled actions

Use scheduled actions to override forecast values for Amazon ECS

Sometimes, you might have additional information about your future application requirements that the forecast calculation is unable to take into account. For example, forecast calculations might underestimate the tasks needed for an upcoming marketing event. You can use scheduled actions to temporarily override the forecast during future time periods. The scheduled actions can run on a recurring basis, or at a specific date and time when there are one-time demand fluctuations.

For example, you can create a scheduled action with a higher number of tasks than what is forecasted. At runtime, Amazon ECS updates the minimum number of tasks in your service. Because predictive scaling optimizes for the number of tasks, a scheduled action with a minimum number of tasks that is higher than the forecast values is honored. This prevents the number of tasks from being less than expected. To stop overriding the forecast, use a second scheduled action to return the minimum number of tasks to its original setting.

The following procedure outlines the steps for overriding the forecast during future time periods.

Topics

Step 1: (Optional) Analyze time series data
Step 2: Create two scheduled actions

Important

This topic assumes that you are trying to override the forecast to scale to a higher capacity than what is forecasted. If you need to temporarily decrease the number of tasks without interference from a predictive scaling policy, use forecast only mode instead. While in forecast only mode, predictive scaling will continue to generate forecasts, but it will not automatically increase the number of tasks. You can then monitor resource utilization and manually decrease the number of tasks as needed.

Step 1: (Optional) Analyze time series data

Start by analyzing the forecast time series data. This is an optional step, but it is helpful if you want to understand the details of the forecast.

Retrieve the forecast

After the forecast is created, you can query for a specific time period in the forecast. The goal of the query is to get a complete view of the time series data for a specific time period.

Your query can include up to two days of future forecast data. If you have been using predictive scaling for a while, you can also access your past forecast data. However, the maximum time duration between the start and end time is 30 days.

To get the forecast using the get-predictive-scaling-forecast AWS CLI command, provide the following parameters in the command:

Enter the name of the cluster name in the resource-id parameter.
Enter the name of the policy in the --policy-name parameter.
Enter the start time in the --start-time parameter to return only forecast data for after or at the specified time.
Enter the end time in the --end-time parameter to return only forecast data for before the specified time.


aws application-autoscaling get-predictive-scaling-forecast \
    --service-namespace ecs \
    --resource-id service/MyCluster/test \
    --policy-name cpu40-predictive-scaling-policy \
    --scalable-dimension ecs:service:DesiredCount \
    --start-time "2021-05-19T17:00:00Z" \
    --end-time "2021-05-19T23:00:00Z"

If successful, the command returns data similar to the following example.


{
    "LoadForecast": [
        {
            "Timestamps": [
                "2021-05-19T17:00:00+00:00",
                "2021-05-19T18:00:00+00:00",
                "2021-05-19T19:00:00+00:00",
                "2021-05-19T20:00:00+00:00",
                "2021-05-19T21:00:00+00:00",
                "2021-05-19T22:00:00+00:00",
                "2021-05-19T23:00:00+00:00"
            ],
            "Values": [
                153.0655799339254,
                128.8288551285919,
                107.1179447150675,
                197.3601844551528,
                626.4039934516954,
                596.9441277518481,
                677.9675713779869
            ],
            "MetricSpecification": {
                "TargetValue": 40.0,
                "PredefinedMetricPairSpecification": {
                    "PredefinedMetricType": "ASGCPUUtilization"
                }
            }
        }
    ],
    "CapacityForecast": {
        "Timestamps": [
            "2021-05-19T17:00:00+00:00",
            "2021-05-19T18:00:00+00:00",
            "2021-05-19T19:00:00+00:00",
            "2021-05-19T20:00:00+00:00",
            "2021-05-19T21:00:00+00:00",
            "2021-05-19T22:00:00+00:00",
            "2021-05-19T23:00:00+00:00"
        ],
        "Values": [
            2.0,
            2.0,
            2.0,
            2.0,
            4.0,
            4.0,
            4.0
        ]
    },
    "UpdateTime": "2021-05-19T01:52:50.118000+00:00"
}

The response includes two forecasts: LoadForecast and CapacityForecast. LoadForecast shows the hourly load forecast. CapacityForecast shows forecast values for the capacity that is needed on an hourly basis to handle the forecasted load while maintaining a TargetValue of 40.0 (40% average CPU utilization).

Identify the target time period

Identify the hour or hours when the one-time demand fluctuation should take place. Remember that dates and times shown in the forecast are in UTC.

Step 2: Create two scheduled actions

Next, create two scheduled actions for a specific time period when your application will have a higher than forecasted load. For example, if you have a marketing event that will drive traffic to your site for a limited period of time, you can schedule a one-time action to update the minimum capacity when it starts. Then, schedule another action to return the minimum capacity to the original setting when the event ends.

Open the console at https://console.aws.amazon.com/ecs/v2.
On the Clusters page, choose the cluster.
On the cluster details page, in the Services section, and then choose the service.

The service details page appears.
Choose Service Auto Scaling.

The policies page appears.
Choose Scheduled actions, and then choose Create.

The Create Schedule action page appears.
For Action name, enter a unique name.
For Time zone, choose a time zone.

All of the time zones listed are from the IANA Time Zone database. For more information, see List of tz database time zones.
For Start time, enter the Date and Time the action starts.
For Recurrence, choose Once.
Under Task adjustments, For Minimum, enter a value less than or equal to the maximum number of tasks..
Choose Create scheduled action.

The policies page appears.
Configure a second scheduled action to return the minimum number of tasks to the original setting at the end of the event. Predictive scaling can scale the number of tasks only when the value you set for Minimum is lower than the forecast values.

To create two scheduled actions for one-time events (AWS CLI)

To use the AWS CLI to create the scheduled actions, use the put-scheduled-update-group-action command.

For example, let's define a schedule that maintains a minimum capacity of three instances on May 19 at 5:00 PM for eight hours. The following commands show how to implement this scenario.

The first put-scheduled-update-group-action command instructs Amazon EC2 Auto Scaling to update the minimum capacity of the specified Auto Scaling group at 5:00 PM UTC on May 19, 2021.


aws autoscaling put-scheduled-update-group-action --scheduled-action-name my-event-start \
  --auto-scaling-group-name my-asg --start-time "2021-05-19T17:00:00Z" --minimum-capacity 3

The second command instructs Amazon EC2 Auto Scaling to set the group's minimum capacity to one at 1:00 AM UTC on May 20, 2021.


aws autoscaling put-scheduled-update-group-action --scheduled-action-name my-event-end \
  --auto-scaling-group-name my-asg --start-time "2021-05-20T01:00:00Z" --minimum-capacity 1

After you add these scheduled actions to the Auto Scaling group, Amazon EC2 Auto Scaling does the following:

At 5:00 PM UTC on May 19, 2021, the first scheduled action runs. If the group currently has fewer than three instances, the group scales out to three instances. During this time and for the next eight hours, Amazon EC2 Auto Scaling can continue to scale out if the predicted capacity is higher than the actual capacity or if there is a dynamic scaling policy in effect.
At 1:00 AM UTC on May 20, 2021, the second scheduled action runs. This returns the minimum capacity to its original setting at the end of the event.

Scaling based on recurring schedules

To override the forecast for the same time period every week, create two scheduled actions and provide the time and date logic using a cron expression.

The cron expression format consists of five fields separated by spaces: [Minute] [Hour] [Day_of_Month] [Month_of_Year] [Day_of_Week]. Fields can contain any allowed values, including special characters.

For example, the following cron expression runs the action every Tuesday at 6:30 AM. The asterisk is used as a wildcard to match all values for a field.


30 6 * * 2