asg.yaml

AWSTemplateFormatVersion: "2010-09-09"

Description: Create Auto Scaling Group

Metadata:
  ParameterGroups:
    - Label:
        default: Export VPC Stack Name
      Parameters:
        - ExportVpcStackName
    - Label:
        default: Export ALB Stack Name
      Parameters:
        - ExportAlbStackName
    - Label:
        default: Email Address
      Parameters:
        - OperatorEMail
    - Label:
        default: Image ID
      Parameters:
        - EC2ImageID
    - Label:
        default: Launch Template Name
      Parameters:
        - WebServerLaunchTemplateName
    - Label:
        default: Instance Type
      Parameters:
        - InstanceType
    - Label:
        default: EC2 KeyPair
      Parameters:
        - EC2KeyName

Parameters:
  ExportVpcStackName:
    Description: The name of the vpc stack that exports values
    Type: String

  ExportAlbStackName:
    Description: The name of the alb stack that exports values
    Type: String

  OperatorEMail:
    Description: A valid EMail address to notify if there are any scaling operations
    Type: String

  EC2KeyName:
    Description: Name of an EC2 KeyPair to enable SSH access to the instance.
    Type: AWS::EC2::KeyPair::KeyName
    ConstraintDescription: Must be the name of an existing EC2 KeyPair.

  EC2ImageID:
    Description: The ID of the custom AMI
    Type: String

  WebServerLaunchTemplateName:
    AllowedPattern: '[a-zA-Z0-9\(\)\.\-/_]+'
    ConstraintDescription: Must be unique to this account. Max 128 chars. No spaces or special characters like '&', '*', '@'.
    Default: Lamp-Server-Launch-Template
    Description: Name of launch template
    Type: String

  InstanceType:
    Description: WebServers EC2 instance type
    Type: String
    Default: t2.micro
    AllowedValues:
      - t1.micro
      - t2.nano
      - t2.micro
      - t2.small
    ConstraintDescription: Must be a valid EC2 instance type.

Resources:
  WebServerLaunchTemplate:
    Type: AWS::EC2::LaunchTemplate
    Properties:
      LaunchTemplateName: !Ref WebServerLaunchTemplateName
      LaunchTemplateData:
        ImageId: !Ref EC2ImageID
        InstanceType: !Ref InstanceType
        KeyName: !Ref EC2KeyName
        Monitoring:
          Enabled: true
        SecurityGroupIds:
          - Fn::ImportValue: !Sub ${ExportVpcStackName}-WebServerSecurityGroup

  NotificationTopic:
    Type: AWS::SNS::Topic
    Properties:
      Subscription:
        - Endpoint: !Ref OperatorEMail
          Protocol: email

  WebServerAutoScalingGroup:
    Type: AWS::AutoScaling::AutoScalingGroup
    Properties:
      AutoScalingGroupName: Auto Scaling Group
      VPCZoneIdentifier:
        - Fn::ImportValue: !Sub ${ExportVpcStackName}-PrivateSubnet1
        - Fn::ImportValue: !Sub ${ExportVpcStackName}-PrivateSubnet2
      HealthCheckGracePeriod: 300
      HealthCheckType: ELB
      LaunchTemplate:
        LaunchTemplateName: !Ref WebServerLaunchTemplateName
        Version: !GetAtt WebServerLaunchTemplate.LatestVersionNumber
      MinSize: 1
      MaxSize: 4
      DesiredCapacity: 2
      Tags:
        - Key: Name
          Value: ASG-WebServer
          PropagateAtLaunch: true
      TargetGroupARNs:
        - Fn::ImportValue: !Sub ${ExportAlbStackName}-ALBTargetGroup
      NotificationConfiguration:
        TopicARN: !Ref NotificationTopic
        NotificationTypes:
          - 'autoscaling:EC2_INSTANCE_LAUNCH'
          - 'autoscaling:EC2_INSTANCE_LAUNCH_ERROR'
          - 'autoscaling:EC2_INSTANCE_TERMINATE'
          - 'autoscaling:EC2_INSTANCE_TERMINATE_ERROR'

  WebServerScaleUpPolicy:
    Type: AWS::AutoScaling::ScalingPolicy
    Properties:
      AdjustmentType: ChangeInCapacity
      AutoScalingGroupName: !Ref WebServerAutoScalingGroup
      Cooldown: 60
      ScalingAdjustment: 1

  WebServerScaleDownPolicy:
    Type: 'AWS::AutoScaling::ScalingPolicy'
    Properties:
      AdjustmentType: ChangeInCapacity
      AutoScalingGroupName: !Ref WebServerAutoScalingGroup
      Cooldown: 60
      ScalingAdjustment: -1

  CPUAlarmHigh:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmDescription: Scale-up if CPU > 90% for 10 minutes
      MetricName: CPUUtilization
      Namespace: AWS/EC2
      Statistic: Average
      Period: 300
      EvaluationPeriods: 2
      Threshold: 90
      AlarmActions:
        - !Ref WebServerScaleUpPolicy
      Dimensions:
        - Name: AutoScalingGroupName
          Value: !Ref WebServerAutoScalingGroup
      ComparisonOperator: GreaterThanThreshold

  CPUAlarmLow:
    Type: 'AWS::CloudWatch::Alarm'
    Properties:
      AlarmDescription: Scale-down if CPU < 70% for 10 minutes
      MetricName: CPUUtilization
      Namespace: AWS/EC2
      Statistic: Average
      Period: 300
      EvaluationPeriods: 2
      Threshold: 70
      AlarmActions:
        - !Ref WebServerScaleDownPolicy
      Dimensions:
        - Name: AutoScalingGroupName
          Value: !Ref WebServerAutoScalingGroup
      ComparisonOperator: LessThanThreshold