AWS Cloudformation for website uptime monitoring

website_uptime_aws_cf.yaml

Parameters: 
  EmailNotification: 
    Type: String
    Description: Enter the destination email to receive the alarms.
  Websiteurl: 
    Type: String
    Description: Enter the website url.
  ScheduleExpression:
    Type: String
    Default: "rate(5 minutes)"

Resources:
  # cloudwatch alarm
  uptimeAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmName: !Join [ "-", [ "My-Website", !Ref Websiteurl, "is-down" ] ]
      AlarmDescription: "Alarm if lambda errors out too many times"
      AlarmActions: [ !Sub "arn:aws:sns:${AWS::Region}:${AWS::AccountId}:MySNSTopic" ]
      Namespace: "AWS/Lambda"
      MetricName: "Errors"
      Dimensions:
      - Name: "FunctionName"
        Value: "UptimeLambdaFunction"
      Statistic: "Average"
      ComparisonOperator: "GreaterThanThreshold"
      Threshold: 0
      EvaluationPeriods: 1
      Period: 300
      TreatMissingData: "missing"

  # sns topic
  MySNSTopic:
    Type: AWS::SNS::Topic
    Properties:
      TopicName: "MySNSTopic"
  
  # sns subscription
  MySubscription:
    Type: AWS::SNS::Subscription
    Properties:
      Endpoint: !Ref EmailNotification
      Protocol: email
      TopicArn: !Ref 'MySNSTopic'
  
  # eventRule for lambda function
  ScheduledRule: 
    Type: AWS::Events::Rule
    Properties: 
      Description: "ScheduledRule"
      ScheduleExpression: !Ref ScheduleExpression
      State: "ENABLED"
      Targets: 
        - 
          Arn: 
            Fn::GetAtt: 
              - "UptimeLambdaFunction"
              - "Arn"
          Id: "TargetFunctionV1"

  PermissionForEventsToInvokeLambda: 
    Type: AWS::Lambda::Permission
    Properties: 
      FunctionName: 
        Ref: "UptimeLambdaFunction"
      Action: "lambda:InvokeFunction"
      Principal: "events.amazonaws.com"
      SourceArn: 
        Fn::GetAtt: 
          - "ScheduledRule"
          - "Arn"

  # lambda execution role
  LambdaExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Principal:
            Service:
            - lambda.amazonaws.com
          Action:
          - sts:AssumeRole
      Policies:
      - PolicyName: allow-logs
        PolicyDocument:
          Version: '2012-10-17'
          Statement:
          - Effect: Allow
            Action:
            - 'logs:*'
            Resource: arn:aws:logs:*:*:*
      - PolicyName: put-cw-data
        PolicyDocument:
          Version: '2012-10-17'
          Statement:
          - Effect: Allow
            Action:
            - 'cloudwatch:PutMetricData'
            Resource: '*'

  # lambda function
  UptimeLambdaFunction:
    Type: AWS::Lambda::Function
    Properties: 
      FunctionName: "UptimeLambdaFunction"
      Handler: "index.handler"
      Runtime: nodejs10.x
      Timeout: 300
      Role:
        Fn::GetAtt:
          - "LambdaExecutionRole"
          - "Arn"
      Code:
        ZipFile: !Sub |
          'use strict';

          var url = require('url');
          var target = '${Websiteurl}';

          exports.handler = function(event, context, callback) {
            var urlObject = url.parse(target);
            var mod = require(
              urlObject.protocol.substring(0, urlObject.protocol.length - 1)
            );
            console.log('[INFO] - Checking ' + target);
            var req = mod.request(urlObject, function(res) {
              res.setEncoding('utf8');
              res.on('data', function(chunk) {
                console.log('[INFO] - Read body chunk');
              });
              res.on('end', function() {
                console.log('[INFO] - Response end');
                callback();
              });
            });

            req.on('error', function(e) {
              console.log('[ERROR] - ' + e.message);
              callback(e);
            });
            req.end();
          };