AWSTemplateFormatVersion: '2010-09-09'

Description: >-
  This template creates Amazon CloudWatch Alarms for Elastic Load Balancer
  Lambda POC. Template creates following resources:
    - One SNS topic to use with composite alarm
    - Two invocation metrics based alarms: (Errors,Invocations)
    - One composite alarm with above two alarm part of it

Metadata:
  AWS::CloudFormation::Interface:
    ParameterGroups:
      - Label:
          default: Alarm Configuation
        Parameters:
          - LambdaFunctionName
          - TopicEmailEndpoint

    ParameterLabels:
      LambdaFunctionName:
        default: Name of Lambda Function
      TopicEmailEndpoint:
        default: Email for SNS Topic        

Parameters:
  LambdaFunctionName:
    Description: Name of Lambda function for which you want to create Alarm
    Type: String
    ConstraintDescription: Must be a valid Lambda funciton name.  
  TopicEmailEndpoint:
    Description: Email for SNS Topic
    Type: String
    ConstraintDescription: Must be a valid email. 

Resources:

  SnsTopic:
    Type: AWS::SNS::Topic
    Properties:
      Subscription:
        - Endpoint: !Ref TopicEmailEndpoint
          Protocol: email
      TopicName: !Join
        - ''
        - - !Ref LambdaFunctionName
          - '-sns-topic'

  LambdaInvocationsAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmDescription: Lambda invocations. Alarms when function invocation reports an error
      AlarmName: !Join
        - ''
        - - !Ref LambdaFunctionName
          - '-invocations'
      ComparisonOperator: LessThanLowerOrGreaterThanUpperThreshold
      EvaluationPeriods: 1
      Metrics:
      - Expression: ANOMALY_DETECTION_BAND(m1, 2)
        Id: ad1
      - Id: m1
        MetricStat:
          Metric:
            Dimensions:
              - Name: FunctionName
                Value: !Ref LambdaFunctionName
            MetricName: Invocations
            Namespace: AWS/Lambda
          Period: !!int 60
          Stat: Sum
      ThresholdMetricId: ad1
      TreatMissingData: breaching

  LambdaErrorsAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmDescription: Lambda errors. Alarm when function reports an error
      AlarmName:  !Join
        - ''
        - - !Ref LambdaFunctionName
          - '-invocations'
      ComparisonOperator: LessThanLowerOrGreaterThanUpperThreshold
      EvaluationPeriods: 1
      Metrics:
      - Expression: ANOMALY_DETECTION_BAND(m1, 2)
        Id: ad1
      - Id: m1
        MetricStat:
          Metric:
            Dimensions:
              - Name: FunctionName
                Value: !Ref LambdaFunctionName         
            MetricName: Errors
            Namespace: AWS/Lambda
          Period: !!int 60
          Stat: Sum
      ThresholdMetricId: ad1
      TreatMissingData: breaching

  LambdaCompositeAlarm:
    Type: AWS::CloudWatch::CompositeAlarm
    DependsOn:
      - LambdaInvocationsAlarm
      - LambdaErrorsAlarm    
    Properties:
      AlarmName: elb-hostname-as-target-monitor
      AlarmRule: !Sub "(ALARM(${LambdaErrorsAlarm}) OR ALARM(${LambdaInvocationsAlarm}))"
      AlarmActions: 
        - !Ref SnsTopic
      AlarmDescription: Lambda composite. Alarm triggers when either of the metric alarms trigger


Outputs:
  ElbSnsTopic:
    Description: 'ELB SNS Topic'
    Value: !GetAtt SnsTopic.TopicName
  ElbLambdaInvocationsAlarm:
    Description: 'ELB Lambda Invocations Alarm'
    Value: !GetAtt LambdaInvocationsAlarm.Arn
  ElbLambdaErrorsAlarm:
    Description: 'ELB Lambda Errors Alarm'
    Value: !GetAtt LambdaErrorsAlarm.Arn
  ElbLambdaCompositeAlarm:
    Description: 'ELB Lambda Composite Alarm'
    Value: !GetAtt LambdaCompositeAlarm.Arn