template.yaml

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: A function triggered by a CloudWatch Alarm.
Outputs:
  AlarmTopicArn:
    Description: The Alarm Topic Arn. This can be provided in other templates to have their alarms invoke this Lambda function.
    Value: !Ref AlarmTopic
Parameters:
  AlarmFunctionName:
    Description: The name of the Alarm Lambda function triggered by the Spending Alarm.
    Default: AlarmFunction
    Type: String
  AlarmTopicName:
    Description: The name of the Alarm Topic.
    Default: AlarmTopic
    Type: String
  AlarmTopicDisplayName:
    Description: The display name of the Alarm Topic.
    Default: AlarmTopic
    Type: String
  SpendingAlarmThreshold:
    Description: The spending threshold before the sample spending alarm is triggered.
    Default: 100
    Type: Number
Resources:
  AlarmFunction:
    Type: AWS::Serverless::Function
    Properties:
      FunctionName: !Ref AlarmFunctionName
      Handler: alarm-function/index.handler
      Runtime: nodejs6.10
      CodeUri: ./build/alarm-function.zip
      Events:
        AlarmTopic: 
          Type: SNS
          Properties:
            Topic: !Ref AlarmTopic
  AlarmTopic:
    Type: AWS::SNS::Topic
    Properties: 
      DisplayName: !Ref AlarmTopicDisplayName
      TopicName: !Ref AlarmTopicName
  AlarmTopicFunctionSubscription:
    Type: AWS::SNS::Subscription
    Properties:
      Endpoint: !GetAtt AlarmFunction.Arn
      Protocol: lambda
      TopicArn: !Ref AlarmTopic
  SpendingAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      Namespace: AWS/Billing
      MetricName: EstimatedCharges
      AlarmDescription: !Sub "Alarm if AWS spending is over ${SpendingAlarmThreshold}"
      Dimensions:
      - Name: Currency
        Value: USD
      Statistic: Maximum
      Period: 21600
      EvaluationPeriods: 1
      Threshold:
        Ref: SpendingAlarmThreshold
      ComparisonOperator: GreaterThanEqualThreshold
      AlarmActions:
      - Ref: AlarmTopic
      InsufficientDataActions:
      - Ref: AlarmTopic