service.yaml

Description: >
    This is an example of a long running ECS service that needs to connect to another ECS service (product-service)
    via it's load balancer. We use environment variables to pass the URL of the product-service to this one's container(s).

Parameters: 

    VPC:
        Description: The VPC that the ECS cluster is deployed to
        Type: AWS::EC2::VPC::Id
        
    Cluster:
        Description: Please provide the ECS Cluster ID that this service should run on
        Type: String

    DesiredCount: 
        Description: How many instances of this task should we run across our cluster?
        Type: Number
        Default: 2

    MaxCount:
        Description: Maximum number of instances of this task we can run across our cluster
        Type: Number
        Default: 3

    ProductServiceUrl:
        Description: The URL of the Product Service (used to fetch product information)
        Type: String

    Listener:
        Description: The Application Load Balancer listener to register with
        Type: String

    Path: 
        Description: The path to register with the Application Load Balancer
        Type: String
        Default: /

    ECSServiceAutoScalingRoleARN:
        Description: The ECS service auto scaling role ARN
        Type: String

Resources:

    Service: 
        Type: AWS::ECS::Service
        DependsOn: ListenerRule
        Properties: 
            Cluster: !Ref Cluster
            Role: !Ref ServiceRole
            DesiredCount: !Ref DesiredCount
            TaskDefinition: !Ref TaskDefinition
            LoadBalancers: 
                - ContainerName: "website-service"
                  ContainerPort: 8000
                  TargetGroupArn: !Ref TargetGroup

    TaskDefinition:
        Type: AWS::ECS::TaskDefinition
        Properties:
            Family: website-service
            ContainerDefinitions:
                - Name: website-service
                  Essential: true
                  Image: 275396840892.dkr.ecr.us-east-1.amazonaws.com/ecs-refarch-cloudformation/website-service:1.0.0
                  Memory: 128
                  Environment: 
                    - Name: PRODUCT_SERVICE_URL
                      Value: !Ref ProductServiceUrl
                  PortMappings:
                    - ContainerPort: 8000
                  LogConfiguration:
                    LogDriver: awslogs
                    Options:
                        awslogs-group: !Ref AWS::StackName
                        awslogs-region: !Ref AWS::Region

    CloudWatchLogsGroup:
        Type: AWS::Logs::LogGroup
        Properties: 
            LogGroupName: !Ref AWS::StackName
            RetentionInDays: 365  

    TargetGroup:
        Type: AWS::ElasticLoadBalancingV2::TargetGroup
        Properties:
            VpcId: !Ref VPC
            Port: 80
            Protocol: HTTP
            Matcher: 
                HttpCode: 200-299
            HealthCheckIntervalSeconds: 10
            HealthCheckPath: /
            HealthCheckProtocol: HTTP
            HealthCheckTimeoutSeconds: 5
            HealthyThresholdCount: 2
    
    ListenerRule:
        Type: AWS::ElasticLoadBalancingV2::ListenerRule
        Properties:
            ListenerArn: !Ref Listener
            Priority: 1
            Conditions:
                - Field: path-pattern
                  Values: 
                    - !Ref Path
            Actions:
                - TargetGroupArn: !Ref TargetGroup
                  Type: forward

    # This IAM Role grants the service access to register/unregister with the 
    # Application Load Balancer (ALB). It is based on the default documented here:
    # http://docs.aws.amazon.com/AmazonECS/latest/developerguide/service_IAM_role.html
    ServiceRole: 
        Type: AWS::IAM::Role
        Properties:
            RoleName: !Sub ecs-service-${AWS::StackName}
            Path: /
            AssumeRolePolicyDocument: |
                {
                    "Statement": [{
                        "Effect": "Allow",
                        "Principal": { "Service": [ "ecs.amazonaws.com" ]},
                        "Action": [ "sts:AssumeRole" ]
                    }]
                }
            Policies:
                - PolicyName: !Sub ecs-service-${AWS::StackName}
                  PolicyDocument:
                    {
                        "Version": "2012-10-17",
                        "Statement": [{
                                "Effect": "Allow",
                                "Action": [
                                    "ec2:AuthorizeSecurityGroupIngress",
                                    "ec2:Describe*",
                                    "elasticloadbalancing:DeregisterInstancesFromLoadBalancer",
                                    "elasticloadbalancing:Describe*",
                                    "elasticloadbalancing:RegisterInstancesWithLoadBalancer",
                                    "elasticloadbalancing:DeregisterTargets",
                                    "elasticloadbalancing:DescribeTargetGroups",
                                    "elasticloadbalancing:DescribeTargetHealth",
                                    "elasticloadbalancing:RegisterTargets"
                                ],
                                "Resource": "*"
                        }]
                    }

    ServiceScalableTarget:
        Type: "AWS::ApplicationAutoScaling::ScalableTarget"
        Properties:
            MaxCapacity: !Ref MaxCount
            MinCapacity: !Ref DesiredCount
            ResourceId: !Join
                - /
                - - service
                  - !Ref Cluster
                  - !GetAtt Service.Name
            RoleARN: !Ref ECSServiceAutoScalingRoleARN
            ScalableDimension: ecs:service:DesiredCount
            ServiceNamespace: ecs

    ServiceScaleOutPolicy:
        Type : "AWS::ApplicationAutoScaling::ScalingPolicy"
        Properties:
            PolicyName: ServiceScaleOutPolicy
            PolicyType: StepScaling
            ScalingTargetId: !Ref ServiceScalableTarget
            StepScalingPolicyConfiguration:
                AdjustmentType: ChangeInCapacity
                Cooldown: 1800
                MetricAggregationType: Average
                StepAdjustments:
                - MetricIntervalLowerBound: 0
                  ScalingAdjustment: 1

    ServiceScaleInPolicy:
        Type : "AWS::ApplicationAutoScaling::ScalingPolicy"
        Properties:
            PolicyName: ServiceScaleInPolicy
            PolicyType: StepScaling
            ScalingTargetId: !Ref ServiceScalableTarget
            StepScalingPolicyConfiguration:
                AdjustmentType: ChangeInCapacity
                Cooldown: 1800
                MetricAggregationType: Average
                StepAdjustments:
                - MetricIntervalUpperBound: 0
                  ScalingAdjustment: -1

    CPUScaleOutAlarm:
        Type: AWS::CloudWatch::Alarm
        Properties:
            AlarmName: CPU utilization greater than 90%
            AlarmDescription: Alarm if cpu utilization greater than 90% of reserved cpu
            Namespace: AWS/ECS
            MetricName: CPUUtilization
            Dimensions:
            - Name: ClusterName
              Value: !Ref Cluster
            - Name: ServiceName
              Value: !GetAtt Service.Name
            Statistic: Maximum
            Period: '60'
            EvaluationPeriods: '3'
            Threshold: '90'
            ComparisonOperator: GreaterThanThreshold
            AlarmActions:
            - !Ref ServiceScaleOutPolicy

    CPUScaleInAlarm:
        Type: AWS::CloudWatch::Alarm
        Properties:
            AlarmName: CPU utilization less than 70%
            AlarmDescription: Alarm if cpu utilization greater than 70% of reserved cpu
            Namespace: AWS/ECS
            MetricName: CPUUtilization
            Dimensions:
            - Name: ClusterName
              Value: !Ref Cluster
            - Name: ServiceName
              Value: !GetAtt Service.Name
            Statistic: Maximum
            Period: '60'
            EvaluationPeriods: '10'
            Threshold: '70'
            ComparisonOperator: LessThanThreshold
            AlarmActions:
            - !Ref ServiceScaleInPolicy