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EC2 Auto Scaling Scheduled Actions

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EC2 Auto Scaling Scheduled Scaling SAA_EN
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EC2 Auto Scaling configuration with scheduled when to scale

This is one of the AWS SAA questions related to the design of a high-performance architecture.
Scheduling Auto Scaling actions to handle anticipated high traffic will lead to stable operation of the system.

In the following pages, we have introduced an Auto Scaling configuration that scales according to CPU utilization.

This is a type of scaling policy called a target tracking scaling policy.

This time, instead of scaling according to specific metrics, we will create a configuration that sets up scheduled actions and automatically scales over a specific period of time.

Environment

Diagram of EC2 Auto Scaling Scheduled Scaling

Create an ALB and attach an Auto Scaling group in a private subnet.
The instance in the group will be Amazon Linux 2, with Apache installed and running as a web server.
Schedule scaling actions to the group. The schedule will temporarily increase the group to 2 with a default instance count of 1.

CloudFormation template files

The above configuration is built with CloudFormation.
The CloudFormation template file is located at the following URL

awstut-saa/02/004 at main · awstut-an-r/awstut-saa
Contribute to awstut-an-r/awstut-saa development by creating an account on GitHub.

Explanation of key points of template files

This configuration is almost the same as the one on the aforementioned page.
This page will cover content related to scheduled scaling actions.

Scheduled Scaling Actions

In order to scale scaling actions, actions at scale-out/in must be defined. The key is to specify the following two points

  • When to take action
  • Number of instances (maximum, minimum, desired)

Scheduled actions for scale-out

Resources: ScheduledActionOut: Type: AWS::AutoScaling::ScheduledAction Properties: AutoScalingGroupName: !Ref AutoScalingGroup DesiredCapacity: !Ref MaxSize MaxSize: !Ref MaxSize MinSize: !Ref MaxSize Recurrence: !Ref ScheduledActionOutRecurrence
Code language: YAML (yaml)

The Recurrence property allows you to schedule actions in a cron expression, but note that the cron expression must be written in UTC, not JST. So, for example, if you want to process at 15:00 every day, you need to write “0 6 * * * *”. This time, set “45 22 * * *” so that the scale-out is performed at 7:45.
You can set the number of instances with the DesiredCapacity, MaxSize, and MinSize properties. This time, specify “2” for the 3 property and set the number of instances to increase from the default of 1 to 2.

Scheduled action for scale-in

Resources: ScheduledActionIn: Type: AWS::AutoScaling::ScheduledAction Properties: AutoScalingGroupName: !Ref AutoScalingGroup DesiredCapacity: !Ref MinSize MaxSize: !Ref MinSize MinSize: !Ref MinSize Recurrence: !Ref ScheduledActionInRecurrence
Code language: YAML (yaml)

The structure is the same as the resource for scheduling out.
Set “50 22 * * *” to the Recurrence property and “1” to the DesiredCapacity, MaxSize, and MinSize properties.

The above settings collectively result in the behavior of increasing the number of instances to 2 between 7:45 and 7:50 daily.

Architecting

Use CloudFormation to build this environment and check the actual behavior.

Create CloudFormation stacks and check resources in stacks

Create CloudFormation stacks.
For information on how to create stacks and check each stack, please refer to the following page

After checking the resources in each stack, the following is the information on the main resources created in this case.

  • DNS name of ALB: saa-02-004-ALB-1864041057.ap-northeast-1.elb.amazonaws.com
  • Auto Scaling Group: saa-02-004-AutoScalingGroup

The AWS Management Console also checks the status of resource creation.
First, check the Auto Scaling group.

Auto Scaling group has been successfully created.

By default, one instance is set to be launched.

Check the Auto Scaling scheduled actions.

Two schedules are set up in the Auto Scaling group.

You can see that two actions are scheduled. One for scale-out and one for scale-in.

Check the history of the Auto Scaling action.

One instance is created in the Auto Scaling group.

One instance has been created as specified.

Check the status of the instance actually created.

One instance is created in the Auto Scaling group.

You can see that one instance has been created as specified in the history.

Accessing ALB1

Now that we are ready, we access the ALB.

Access to Instance 1.

A response is received from the created instance.
You can see that the Auto Scaling group has been successfully attached to the ALB.

Scale-out behavior

Next, we will check the behavior during scale-out.
We will wait until 7:45, when scale-out starts, before checking.
First, check the action history of the Auto Scaling group.

Scheduled actions initiated scale-out.

The action started at 7:45 as scheduled, and the second instance was created.

Check the instances in the Auto Scaling group again.

The number of instances increased to two.

You can see that the second instance has been created.
We have indeed been able to scale out the number of instances with the scheduled action.

Accessing ALB2

Access the ALB again.

Access to Instance 2.

A response is now returned from the second instance.

Scale-in behavior

Finally, we will check the behavior during scale-in.
We will wait until 7:50, when scale-in starts, before checking.
First, check the action history of the Auto Scaling group.

Scheduled actions initiated scale-in.

The action started at 7:50 as scheduled, and one of the two instances has finished.

Check the instances in the Auto Scaling group again.

The number of instances returned to one.

You can see that only one instance is deployed in the Auto Scaling group.
We have indeed been able to scale in the number of instances with the scheduled action.

Summary

We have set up a scheduled action for the Auto Scaling group and verified the configuration to automatically scale to a specific time period.

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