How to Set Scaling Policy in AWS: Step-by-Step Guide

To set a scaling policy in AWS, create an Auto Scaling group and define a scaling policy that adjusts capacity based on metrics like CPU usage. Use the AWS Management Console, CLI, or SDK to specify the policy type (target tracking, step scaling, or simple scaling) and thresholds for scaling actions.

Syntax

A scaling policy in AWS Auto Scaling typically includes these parts:

• Auto Scaling Group: The group of instances to scale.
• Policy Name: A unique name for the scaling policy.
• Policy Type: Defines how scaling happens (e.g., target tracking, step scaling).
• Metric and Threshold: The metric to monitor (like CPU utilization) and the value that triggers scaling.
• Scaling Adjustment: How much to add or remove instances.

bash

aws autoscaling put-scaling-policy \
  --auto-scaling-group-name MyAutoScalingGroup \
  --policy-name MyScalingPolicy \
  --policy-type TargetTrackingScaling \
  --target-tracking-configuration file://target-tracking.json

Example

This example creates a target tracking scaling policy that keeps average CPU usage at 50% for an Auto Scaling group named MyAutoScalingGroup.

json

{
  "PredefinedMetricSpecification": {
    "PredefinedMetricType": "ASGAverageCPUUtilization"
  },
  "TargetValue": 50.0
}

Example (CLI Command)

Use this AWS CLI command with the above JSON saved as target-tracking.json:

bash

aws autoscaling put-scaling-policy \
  --auto-scaling-group-name MyAutoScalingGroup \
  --policy-name Cpu50PercentPolicy \
  --policy-type TargetTrackingScaling \
  --target-tracking-configuration file://target-tracking.json

Output

{
    "PolicyARN": "arn:aws:autoscaling:region:account-id:scalingPolicy:policy-id:autoScalingGroupName/MyAutoScalingGroup:policyName/Cpu50PercentPolicy"
}

Common Pitfalls

• Not attaching the scaling policy to an Auto Scaling group causes no effect.
• Using incorrect metric names or thresholds can prevent scaling actions.
• For step scaling, missing cooldown periods can cause rapid scaling up and down.
• Not having proper IAM permissions blocks policy creation.

bash

aws autoscaling put-scaling-policy \
  --auto-scaling-group-name WrongGroupName \
  --policy-name MyPolicy \
  --policy-type TargetTrackingScaling \
  --target-tracking-configuration file://target-tracking.json

# Correct usage:
aws autoscaling put-scaling-policy \
  --auto-scaling-group-name MyAutoScalingGroup \
  --policy-name MyPolicy \
  --policy-type TargetTrackingScaling \
  --target-tracking-configuration file://target-tracking.json

Quick Reference

Key points to remember when setting scaling policies in AWS:

• Policy Types: Target Tracking (recommended), Step Scaling, Simple Scaling.
• Metrics: Use predefined metrics like CPU, Network, or custom CloudWatch metrics.
• Cooldown: Set cooldown periods to avoid rapid scaling.
• Permissions: Ensure your IAM user/role has autoscaling:PutScalingPolicy permission.

Key Takeaways

Create a scaling policy attached to an Auto Scaling group to automate resource scaling.

Use target tracking policies for simple, automatic scaling based on metrics like CPU usage.

Always verify metric names, thresholds, and IAM permissions to avoid errors.

Set cooldown periods to prevent frequent scaling actions.

Test scaling policies in a safe environment before production deployment.