template.yml

---
AWSTemplateFormatVersion: '2010-09-09'
Transform: 'AWS::Serverless-2016-10-31'
Description: 'CloudWatch Alarm to Teams'
Parameters:
  WebhookURL:
    Description: 'Teams incoming webhook URL'
    Type: String
Resources:
  ForwardAlarmFunction:
    Type: 'AWS::Serverless::Function'
    Properties:
      Handler: 'handler.processEvent'
      Runtime: 'nodejs12.x'
      MemorySize: 512
      Timeout: 30
      Environment:
        Variables:
          WEBHOOK_URL: !Ref WebhookURL
      Events:
        EventRule:
          Type: EventBridgeRule
          Properties:
            Pattern:
              source:
              - 'aws.cloudwatch'
              'detail-type':
              - 'CloudWatch Alarm State Change'
              detail:
                state:
                  value:
                  - ALARM
      Policies:
      - !Ref ForwardAlarmPolicy
  ForwardAlarmPolicy:
    Type: 'AWS::IAM::ManagedPolicy'
    Properties:
      PolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Action: 'cloudwatch:describeAlarms'
          Resource: '*'