AWS CloudFormation Auto Scaling Skill

AWS CloudFormation Auto Scaling

Overview

Create production-ready Auto Scaling infrastructure using AWS CloudFormation templates. This skill covers Auto Scaling Groups for EC2, ECS, and Lambda, launch configurations, launch templates, scaling policies, lifecycle hooks, and best practices for high availability and cost optimization.

When to Use

Use this skill when:

Creating Auto Scaling Groups for EC2 instances
Configuring Launch Configurations or Launch Templates
Implementing scaling policies (step, target tracking, simple)
Adding lifecycle hooks for lifecycle management
Creating scaling for ECS services
Implementing Lambda provisioned concurrency scaling
Organizing templates with Parameters, Outputs, Mappings, Conditions
Implementing cross-stack references with export/import
Using mixed instances policies for diversity

Instructions

Follow these steps to create Auto Scaling infrastructure with CloudFormation:

1. Define Parameters

Specify capacity and instance settings with AWS-specific parameter types:

Parameters:
  MinSize:
    Type: Number
    Default: 2
    Description: Minimum number of instances

  MaxSize:
    Type: Number
    Default: 10
    Description: Maximum number of instances

  DesiredCapacity:
    Type: Number
    Default: 2
    Description: Desired number of instances

  InstanceType:
    Type: AWS::EC2::Instance::Type
    Default: t3.micro
    Description: EC2 instance type

  AmiId:
    Type: AWS::EC2::Image::Id
    Description: AMI ID for instances

  SubnetIds:
    Type: List<AWS::EC2::Subnet::Id>
    Description: Subnets for Auto Scaling group

2. Create Launch Configuration

Define instance launch settings:

Resources:
  MyLaunchConfiguration:
    Type: AWS::AutoScaling::LaunchConfiguration
    Properties:
      LaunchConfigurationName: !Sub "${AWS::StackName}-lc"
      ImageId: !Ref AmiId
      InstanceType: !Ref InstanceType
      KeyName: !Ref KeyName
      SecurityGroups:
        - !Ref InstanceSecurityGroup
      InstanceMonitoring: Enabled
      UserData:
        Fn::Base64: |
          #!/bin/bash
          yum update -y
          yum install -y httpd
          systemctl start httpd

3. Create Auto Scaling Group

Specify min/max/desired capacity and networking:

Resources:
  MyAutoScalingGroup:
    Type: AWS::AutoScaling::AutoScalingGroup
    Properties:
      AutoScalingGroupName: !Sub "${AWS::StackName}-asg"
      MinSize: !Ref MinSize
      MaxSize: !Ref MaxSize
      DesiredCapacity: !Ref DesiredCapacity
      VPCZoneIdentifier: !Ref SubnetIds
      LaunchConfigurationName: !Ref MyLaunchConfiguration
      TargetGroupARNs:
        - !Ref MyTargetGroup
      HealthCheckType: ELB
      HealthCheckGracePeriod: 300
      Tags:
        - Key: Environment
          Value: !Ref Environment
          PropagateAtLaunch: true

4. Configure Load Balancer Integration

Set up ALB for traffic distribution:

Resources:
  MyTargetGroup:
    Type: AWS::ElasticLoadBalancingV2::TargetGroup
    Properties:
      Name: !Sub "${AWS::StackName}-tg"
      Port: 80
      Protocol: HTTP
      VpcId: !Ref VPCId
      HealthCheckPath: /
      TargetType: instance

  MyLoadBalancer:
    Type: AWS::ElasticLoadBalancingV2::LoadBalancer
    Properties:
      Name: !Sub "${AWS::StackName}-alb"
      Scheme: internet-facing
      Type: application
      Subnets:
        - !Ref PublicSubnet1
        - !Ref PublicSubnet2

5. Add Scaling Policies

Implement target tracking scaling:

Resources:
  TargetTrackingPolicy:
    Type: AWS::AutoScaling::ScalingPolicy
    Properties:
      PolicyName: !Sub "${AWS::StackName}-target-tracking"
      PolicyType: TargetTrackingScaling
      AutoScalingGroupName: !Ref MyAutoScalingGroup
      TargetTrackingConfiguration:
        PredefinedMetricSpecification:
          PredefinedMetricType: ASGAverageCPUUtilization
        TargetValue: 70
        DisableScaleIn: false

6. Configure Lifecycle Hooks

Implement hooks for graceful instance management:

Resources:
  LifecycleHookTermination:
    Type: AWS::AutoScaling::LifecycleHook
    Properties:
      LifecycleHookName: !Sub "${AWS::StackName}-termination-hook"
      AutoScalingGroupName: !Ref MyAutoScalingGroup
      LifecycleTransition: autoscaling:EC2_INSTANCE_TERMINATING
      HeartbeatTimeout: 300
      NotificationTargetARN: !Ref SNSTopic
      RoleARN: !Ref LifecycleHookRole

7. Set Up Monitoring

Configure CloudWatch alarms for scaling triggers:

Resources:
  HighCpuAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmName: !Sub "${AWS::StackName}-high-cpu"
      MetricName: CPUUtilization
      Namespace: AWS/EC2
      Dimensions:
        - Name: AutoScalingGroupName
          Value: !Ref MyAutoScalingGroup
      Statistic: Average
      Period: 60
      EvaluationPeriods: 3
      Threshold: 70
      ComparisonOperator: GreaterThanThreshold

8. Configure Outputs and Cross-Stack References

Export ASG configuration for other stacks:

Outputs:
  AutoScalingGroupName:
    Description: Name of the Auto Scaling Group
    Value: !Ref MyAutoScalingGroup
    Export:
      Name: !Sub "${AWS::StackName}-AutoScalingGroupName"

  AutoScalingGroupArn:
    Description: ARN of the Auto Scaling Group
    Value: !GetAtt MyAutoScalingGroup.AutoScalingGroupArn
    Export:
      Name: !Sub "${AWS::StackName}-AutoScalingGroupArn"

Examples

Complete Auto Scaling Template

Full end-to-end template with VPC, ASG, ALB, and scaling policies:

AWSTemplateFormatVersion: '2010-09-09'
Description: Auto Scaling Group with ALB integration

Parameters:
  Environment:
    Type: String
    Default: production
  InstanceType:
    Type: AWS::EC2::Instance::Type
    Default: t3.micro
  AmiId:
    Type: AWS::EC2::Image::Id
  VpcId:
    Type: AWS::EC2::VPC::Id
  SubnetIds:
    Type: List<AWS::EC2::Subnet::Id>

Resources:
  InstanceSecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Security group for ASG instances
      VpcId: !Ref VpcId
      SecurityGroupEgress:
        - CidrIp: 0.0.0.0/0
          IpProtocol: "-1"

  TargetGroup:
    Type: AWS::ElasticLoadBalancingV2::TargetGroup
    Properties:
      Name: !Sub "${AWS::StackName}-tg"
      Port: 80
      Protocol: HTTP
      VpcId: !Ref VpcId
      HealthCheckPath: /health
      TargetType: instance

  LaunchTemplate:
    Type: AWS::EC2::LaunchTemplate
    Properties:
      LaunchTemplateName: !Sub "${AWS::StackName}-lt"
      ImageId: !Ref AmiId
      InstanceType: !Ref InstanceType
      SecurityGroupIds:
        - !Ref InstanceSecurityGroup

  AutoScalingGroup:
    Type: AWS::AutoScaling::AutoScalingGroup
    Properties:
      AutoScalingGroupName: !Sub "${AWS::StackName}-asg"
      MinSize: 2
      MaxSize: 10
      DesiredCapacity: 4
      LaunchTemplate:
        LaunchTemplateId: !Ref LaunchTemplate
        Version: !GetAtt LaunchTemplate.LatestVersionNumber
      VPCZoneIdentifier: !Ref SubnetIds
      TargetGroupARNs:
        - !Ref TargetGroup
      HealthCheckType: ELB
      HealthCheckGracePeriod: 300
      Tags:
        - Key: Name
          Value: !Sub "${AWS::StackName}-instance"
          PropagateAtLaunch: true

  ScalingPolicy:
    Type: AWS::AutoScaling::ScalingPolicy
    Properties:
      PolicyName: !Sub "${AWS::StackName}-cpu-policy"
      PolicyType: TargetTrackingScaling
      AutoScalingGroupName: !Ref AutoScalingGroup
      TargetTrackingConfiguration:
        PredefinedMetricSpecification:
          PredefinedMetricType: ASGAverageCPUUtilization
        TargetValue: 70

Outputs:
  AutoScalingGroupName:
    Value: !Ref AutoScalingGroup
    Export:
      Name: !Sub "${AWS::StackName}-ASG-Name"

Validation Commands

Validate template and test changes before deployment:

# Validate CloudFormation template
aws cloudformation validate-template --template-body file://template.yaml

# Create change set to preview changes
aws cloudformation create-change-set \
  --stack-name my-asg-stack \
  --template-body file://template.yaml \
  --change-set-type CREATE

# Describe change set
aws cloudformation describe-change-set \
  --stack-name my-asg-stack \
  --change-set-name <change-set-id>

# Execute change set
aws cloudformation execute-change-set \
  --stack-name my-asg-stack \
  --change-set-name <change-set-id>

Verification Commands

Verify ASG health and configuration after deployment:

# Describe Auto Scaling Groups
aws autoscaling describe-auto-scaling-groups \
  --auto-scaling-group-names my-asg-stack-asg

# Check instance health
aws autoscaling describe-auto-scaling-instances \
  --instance-ids <instance-id>

# Verify scaling policies
aws autoscaling describe-policies \
  --auto-scaling-group-name my-asg-stack-asg

# Review scaling activities
aws autoscaling describe-scaling-activities \
  --auto-scaling-group-name my-asg-stack-asg

Constraints and Warnings

Resource Limits

ASG max size: 10000 instances (request limit increase for more)
Max 20 launch configurations per account (use Launch Templates instead)
Lifecycle hooks: 50 per ASG
Scaling policies: 20 per ASG (Target Tracking limit)
Cooldown period: 300 seconds default (decrease cautiously)

Operational Warnings

Do not update both Launch Configuration and Launch Template on the same ASG in one update
Always use UpdatePolicy for graceful updates and instance refresh
Set HealthCheckGracePeriod >= expected instance initialization time
Lifecycle hook timeout must accommodate graceful shutdown procedures
Spot Instances: set InstanceMaintenancePolicy to avoid unexpected terminations

Security Warnings

Never hardcode credentials; use IAM instance profiles
Use Service-Linked Roles for Auto Scaling (aws-autoscaling.amazonaws.com)
Restrict ASG describe permissions to prevent information disclosure
KMS keys for EBS encryption must be created in same region as ASG
Cross-stack references export names must be unique per region

Best Practices

High Availability

Distribute instances across multiple AZs
Use ALB with health checks for automatic routing
Implement lifecycle hooks for graceful shutdown
Configure appropriate termination policies
Use mixed instances policies for diversity
Set appropriate health check grace periods

Cost Optimization

Use Spot Instances for fault-tolerant workloads
Implement right-sizing of instances
Configure aggressive scale-in policies
Use scheduled scaling for predictable patterns
Monitor and optimize regularly
Set appropriate minimum capacity to avoid over-provisioning

Monitoring

Create CloudWatch Alarms for key metrics
Implement scaling policies based on metrics
Use lifecycle hooks for logging and analytics
Configure SNS notifications for scaling events
Implement detailed monitoring for troubleshooting
Use multiple scaling policies for optimal response

Security

Use IAM roles with least privilege permissions
Encrypt EBS volumes with KMS
Configure restrictive security groups
Use VPC with appropriate subnets
Implement Parameter Store for sensitive configuration
Avoid broad managed policies (use specific permissions)
Configure appropriate instance profiles

References

For detailed implementation guidance, see:

constraints.md - Resource limits (ASG limits, scaling policy limits, lifecycle hook limits), scaling constraints (cooldown periods, health check grace periods, min/max capacity), operational constraints (mixed instances policy, predictive scaling, instance refresh), security constraints (IAM roles, service-linked roles, KMS permissions), and cost considerations (Spot instance termination, over-provisioning, scaling frequency)

Agent Skills: AWS CloudFormation Auto Scaling

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