service.yml

AWSTemplateFormatVersion: '2010-09-09'
Parameters:
  StackName:
    Type: String
    Default: ""
    Description: The environment name
  ServiceName:
    Type: String
    Description: A name for the service
  ImageUrl:
    Type: String
    Description: The url of a docker image that is the application for this service
  TaskRole:
    Type: String
    Default: ""
    Description: A task role to grant to the service container
  ListenerArn:
    Type: String
    Default: ""
    Description: The load balancer listener to add the service to
  Path:
    Type: String
    Default: ""
    Description: A path on the load balancer that this service should be connected to
  Priority:
    Type: Number
    Default: 0
    Description: The priority of the rule that is added to the load balancer
  DesiredCount:
    Type: Number
    Default: 2
    Description: How many copies of the service task to run

# Determine whether or not to create a service that is attached to a load balancer
Conditions:
  AttachedToLoadBalancer: !Not [ !Equals [!Ref 'Path', ''] ]

Resources:
  # A log group for storing the container logs for this service
  LogGroup:
    Type: AWS::Logs::LogGroup
    Properties:
      LogGroupName: !Join ['-', [!Ref 'StackName', 'service', !Ref 'ServiceName']]

  # The task definition that describes how to run the docker container
  TaskDefinition:
    Type: AWS::ECS::TaskDefinition
    Properties:
      Family: !Ref 'ServiceName'
      TaskRoleArn: !Ref TaskRole
      ContainerDefinitions:
        - Name: !Ref 'ServiceName'
          Cpu: 256
          Memory: 256
          Image: !Ref 'ImageUrl'
          PortMappings:
            - ContainerPort: 8081
              HostPort: 0
          Environment:
            - Name: 'EXTERNAL_URL'
              Value:
                Fn::ImportValue:
                  !Join [':', [!Ref 'StackName', 'ExternalUrl']]
            - Name: 'NODE_ENV'
              Value: 'production'
            - Name: 'REGION'
              Value: !Ref 'AWS::Region'
          LogConfiguration:
            LogDriver: 'awslogs'
            Options:
              awslogs-group: !Join ['-', [!Ref 'StackName', 'service', !Ref 'ServiceName']]
              awslogs-region: !Ref 'AWS::Region'
              awslogs-stream-prefix: !Ref 'ServiceName'

  # Create an ECS service that isn't attached to a loadbalancer
  Service:
    Type: AWS::ECS::Service
    DependsOn:
      - LogGroup
    Properties:
      Cluster:
        Fn::ImportValue:
          !Join [':', [!Ref 'StackName', 'ClusterName']]
      DeploymentConfiguration:
        MaximumPercent: 200
        MinimumHealthyPercent: 75
      PlacementStrategies:
        - Type: spread
          Field: attribute:ecs.availability-zone
        - Type: binpack
          Field: cpu
      DesiredCount: !Ref 'DesiredCount'
      ServiceName:
        # The following statements always produces the same value for
        # the service name, but the select exists as a hack to conditionally
        # introduce a dependency on the load balancer rule if the service is
        # attached to a load balancer. This hack is necessary because the service
        # depends on the load balancer rule only if attached to a load balancer
        # but the normal DependsOn property only accepts a static value, no
        # conditionals possible.
        Fn::If:
          - 'AttachedToLoadBalancer'
          - Fn::Select:
            - 0
            - [!Ref 'ServiceName', !Ref 'LoadBalancerRule']
          - !Ref 'ServiceName'
      TaskDefinition: !Ref 'TaskDefinition'
      Role:
        Fn::If:
          - 'AttachedToLoadBalancer'
          - Fn::ImportValue:
              !Join [':', [!Ref 'StackName', 'ECSRole']]
          - !Ref "AWS::NoValue"
      LoadBalancers:
        Fn::If:
          - 'AttachedToLoadBalancer'
          - - ContainerName: !Ref 'ServiceName'
              ContainerPort: 8081
              TargetGroupArn: !Ref 'TargetGroup'
          - []

  # Create a target group for tracking this task across the cluster
  TargetGroup:
    Type: AWS::ElasticLoadBalancingV2::TargetGroup
    Condition: AttachedToLoadBalancer
    Properties:
      HealthCheckIntervalSeconds: 6
      HealthCheckPath: /
      HealthCheckProtocol: HTTP
      HealthCheckTimeoutSeconds: 5
      HealthyThresholdCount: 2
      Name: !Ref 'ServiceName'
      Port: 80
      Protocol: HTTP
      UnhealthyThresholdCount: 2
      VpcId:
        Fn::ImportValue:
          !Join [':', [!Ref 'StackName', 'VPCId']]

  # Create a rule on the load balancer for routing traffic to the target group
  LoadBalancerRule:
    Type: AWS::ElasticLoadBalancingV2::ListenerRule
    Condition: AttachedToLoadBalancer
    Properties:
      Actions:
        - TargetGroupArn: !Ref 'TargetGroup'
          Type: 'forward'
      Conditions:
        - Field: path-pattern
          Values: [!Ref 'Path']
      ListenerArn: !Ref 'ListenerArn'
      Priority: !Ref 'Priority'

  # Enable autoscaling for this service
  ScalableTarget:
    Type: AWS::ApplicationAutoScaling::ScalableTarget
    DependsOn: Service
    Properties:
      ServiceNamespace: 'ecs'
      ScalableDimension: 'ecs:service:DesiredCount'
      ResourceId:
        Fn::Join:
          - '/'
          - - service
            - Fn::ImportValue: !Join [':', [!Ref 'StackName', 'ClusterName']]
            - !Ref 'ServiceName'
      MinCapacity: 2
      MaxCapacity: 10
      RoleARN:
        Fn::ImportValue:
          !Join [':', [!Ref 'StackName', 'AutoscalingRole']]

  # Create scaling policies for the service
  ScaleDownPolicy:
    Type: AWS::ApplicationAutoScaling::ScalingPolicy
    DependsOn: ScalableTarget
    Properties:
      PolicyName:
        Fn::Join:
          - '/'
          - - scale
            - !Ref 'StackName'
            - !Ref 'ServiceName'
            - down
      PolicyType: StepScaling
      ResourceId:
        Fn::Join:
          - '/'
          - - service
            - Fn::ImportValue: !Join [':', [!Ref 'StackName', 'ClusterName']]
            - !Ref 'ServiceName'
      ScalableDimension: 'ecs:service:DesiredCount'
      ServiceNamespace: 'ecs'
      StepScalingPolicyConfiguration:
        AdjustmentType: 'ChangeInCapacity'
        StepAdjustments:
          - MetricIntervalLowerBound: 0
            ScalingAdjustment: -1
        MetricAggregationType: 'Average'
        Cooldown: 60

  ScaleUpPolicy:
    Type: AWS::ApplicationAutoScaling::ScalingPolicy
    DependsOn: ScalableTarget
    Properties:
      PolicyName:
        Fn::Join:
          - '/'
          - - scale
            - !Ref 'StackName'
            - !Ref 'ServiceName'
            - up
      PolicyType: StepScaling
      ResourceId:
        Fn::Join:
          - '/'
          - - service
            - Fn::ImportValue: !Join [':', [!Ref 'StackName', 'ClusterName']]
            - !Ref 'ServiceName'
      ScalableDimension: 'ecs:service:DesiredCount'
      ServiceNamespace: 'ecs'
      StepScalingPolicyConfiguration:
        AdjustmentType: 'ChangeInCapacity'
        StepAdjustments:
          - MetricIntervalLowerBound: 0
            MetricIntervalUpperBound: 20
            ScalingAdjustment: 1
          - MetricIntervalLowerBound: 20
            ScalingAdjustment: 2
        MetricAggregationType: 'Average'
        Cooldown: 60

  # Create alarms to trigger these policies
  LowCpuUsageAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmName:
        Fn::Join:
          - '-'
          - - low-cpu
            - !Ref 'StackName'
            - !Ref 'ServiceName'
      AlarmDescription:
        Fn::Join:
          - ' '
          - - "Low CPU utilization for service"
            - !Ref 'ServiceName'
            - "in stack"
            - !Ref 'StackName'
      MetricName: CPUUtilization
      Namespace: AWS/ECS
      Dimensions:
        - Name: ServiceName
          Value: !Ref 'ServiceName'
        - Name: ClusterName
          Value:
            Fn::ImportValue: !Join [':', [!Ref 'StackName', 'ClusterName']]
      Statistic: Average
      Period: 60
      EvaluationPeriods: 1
      Threshold: 20
      ComparisonOperator: LessThanOrEqualToThreshold
      AlarmActions:
        - !Ref ScaleDownPolicy

  HighCpuUsageAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmName:
        Fn::Join:
          - '-'
          - - high-cpu
            - !Ref 'StackName'
            - !Ref 'ServiceName'
      AlarmDescription:
        Fn::Join:
          - ' '
          - - "High CPU utilization for service"
            - !Ref 'ServiceName'
            - "in stack"
            - !Ref 'StackName'
      MetricName: CPUUtilization
      Namespace: AWS/ECS
      Dimensions:
        - Name: ServiceName
          Value: !Ref 'ServiceName'
        - Name: ClusterName
          Value:
            Fn::ImportValue: !Join [':', [!Ref 'StackName', 'ClusterName']]
      Statistic: Average
      Period: 60
      EvaluationPeriods: 1
      Threshold: 70
      ComparisonOperator: GreaterThanOrEqualToThreshold
      AlarmActions:
        - !Ref ScaleUpPolicy