AWSTemplateFormatVersion: '2010-09-09'
Description: Add autoscaling rules that scale an ECS service based on CPU utilization
Parameters:
  ClusterName:
    Type: String
    Default: default
    Description: The cluster that is running the service you want to scale
  ServiceName:
    Type: String
    Default: nginx
    Description: The name of the service to scale

Resources:

  # Role that Application Auto Scaling will use to interact with
  # CloudWatch and Amazon ECS
  AutoscalingRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Statement:
        - Effect: Allow
          Principal:
            Service: [application-autoscaling.amazonaws.com]
          Action: ['sts:AssumeRole']
      Path: /
      Policies:
      - PolicyName: service-autoscaling
        PolicyDocument:
          Statement:
          - Effect: Allow
            Action:
              - 'application-autoscaling:*'
              - 'cloudwatch:DescribeAlarms'
              - 'cloudwatch:PutMetricAlarm'
              - 'ecs:DescribeServices'
              - 'ecs:UpdateService'
            Resource: '*'

  # Enable autoscaling for the service
  ScalableTarget:
    Type: AWS::ApplicationAutoScaling::ScalableTarget
    Properties:
      ServiceNamespace: 'ecs'
      ScalableDimension: 'ecs:service:DesiredCount'
      ResourceId: !Sub 'service/${ClusterName}/${ServiceName}'
      MinCapacity: 2
      MaxCapacity: 10
      RoleARN: !GetAtt AutoscalingRole.Arn

  # Create scaling policies that describe how to scale the service up and down.
  ScaleDownPolicy:
    Type: AWS::ApplicationAutoScaling::ScalingPolicy
    DependsOn: ScalableTarget
    Properties:
      PolicyName: !Sub scale-${ClusterName}-${ServiceName}-down
      PolicyType: StepScaling
      ResourceId: !Sub 'service/${ClusterName}/${ServiceName}'
      ScalableDimension: 'ecs:service:DesiredCount'
      ServiceNamespace: 'ecs'
      StepScalingPolicyConfiguration:
        AdjustmentType: 'ChangeInCapacity'
        StepAdjustments:
          - MetricIntervalUpperBound: 0
            ScalingAdjustment: -1
        MetricAggregationType: 'Average'
        Cooldown: 60

  ScaleUpPolicy:
    Type: AWS::ApplicationAutoScaling::ScalingPolicy
    DependsOn: ScalableTarget
    Properties:
      PolicyName: !Sub scale-${ClusterName}-${ServiceName}-up
      PolicyType: StepScaling
      ResourceId: !Sub 'service/${ClusterName}/${ServiceName}'
      ScalableDimension: 'ecs:service:DesiredCount'
      ServiceNamespace: 'ecs'
      StepScalingPolicyConfiguration:
        AdjustmentType: 'ChangeInCapacity'
        StepAdjustments:
          - MetricIntervalLowerBound: 0
            MetricIntervalUpperBound: 15
            ScalingAdjustment: 1
          - MetricIntervalLowerBound: 15
            MetricIntervalUpperBound: 25
            ScalingAdjustment: 2
          - MetricIntervalLowerBound: 25
            ScalingAdjustment: 3
        MetricAggregationType: 'Average'
        Cooldown: 60

  # Create alarms to trigger the scaling policies
  LowCpuUsageAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmName: !Sub low-cpu-${ClusterName}-${ServiceName}
      AlarmDescription: !Sub "Low CPU utilization for service ${ServiceName} in cluster ${ClusterName}"
      MetricName: CPUUtilization
      Namespace: AWS/ECS
      Dimensions:
        - Name: ServiceName
          Value: !Ref 'ServiceName'
        - Name: ClusterName
          Value: !Ref 'ClusterName'
      Statistic: Average
      Period: 60
      EvaluationPeriods: 1
      Threshold: 20
      ComparisonOperator: LessThanOrEqualToThreshold
      AlarmActions:
        - !Ref ScaleDownPolicy

  HighCpuUsageAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmName: !Sub high-cpu-${ClusterName}-${ServiceName}
      AlarmDescription: !Sub "High CPU utilization for service ${ServiceName} in cluster ${ClusterName}"
      MetricName: CPUUtilization
      Namespace: AWS/ECS
      Dimensions:
        - Name: ServiceName
          Value: !Ref 'ServiceName'
        - Name: ClusterName
          Value: !Ref 'ClusterName'
      Statistic: Average
      Period: 60
      EvaluationPeriods: 1
      Threshold: 70
      ComparisonOperator: GreaterThanOrEqualToThreshold
      AlarmActions:
        - !Ref ScaleUpPolicy