A basic CloudFormation template for an RDS Aurora cluster.

RDS-Aurora-CloudFormation-Example.yaml

---
AWSTemplateFormatVersion: 2010-09-09

Description: >
  A basic CloudFormation template for an RDS Aurora cluster.

Parameters:
  DatabaseUsername:
    AllowedPattern: "[a-zA-Z0-9]+"
    ConstraintDescription: must be between 1 to 16 alphanumeric characters.
    Description: The database admin account user name, between 1 to 16 alphanumeric characters.
    MaxLength: '16'
    MinLength: '1'
    Type: String
  DatabasePassword:
    AllowedPattern: "[a-zA-Z0-9]+"
    ConstraintDescription: must be between 8 to 41 alphanumeric characters.
    Description: The database admin account password, between 8 to 41 alphanumeric characters.
    MaxLength: '41'
    MinLength: '8'
    NoEcho: 'true'
    Type: String

Mappings:
  '000000000000':
    us-east-1:
      Subnets:
        - subnet-00000000
        - subnet-11111111
        - subnet-22222222
      SecurityGroups:
        - sg-00000000
      InstanceType: db.r4.large
      BackupRetentionPeriod: 7

Metadata:
  AWS::CloudFormation::Interface:
    ParameterGroups:
      - Label:
          default: Database Configuration
        Parameters:
          - DatabaseUsername
          - DatabasePassword
    ParameterLabels:
      DatabaseUsername:
        default: Database Username
      DatabasePassword:
        default: Database Password

Resources:
  StackAlarmTopic:
    Type: AWS::SNS::Topic
    Properties:
      DisplayName: Stack Alarm Topic

  DatabaseSubnetGroup:
    Type: AWS::RDS::DBSubnetGroup
    Properties:
      DBSubnetGroupDescription: CloudFormation managed DB subnet group.
      SubnetIds: !FindInMap [!Ref "AWS::AccountId", !Ref "AWS::Region", "Subnets"]

  DatabaseCluster:
    Type: AWS::RDS::DBCluster
    Properties:
      Engine: aurora
      MasterUsername: !Ref "DatabaseUsername"
      MasterUserPassword: !Ref "DatabasePassword"
      BackupRetentionPeriod: !FindInMap [!Ref "AWS::AccountId", !Ref "AWS::Region", "BackupRetentionPeriod"]
      PreferredBackupWindow: 01:00-02:00
      PreferredMaintenanceWindow: mon:03:00-mon:04:00
      DBSubnetGroupName: !Ref "DatabaseSubnetGroup"
      VpcSecurityGroupIds: !FindInMap [!Ref "AWS::AccountId", !Ref "AWS::Region", "SecurityGroups"]

  DatabasePrimaryInstance:
    Type: AWS::RDS::DBInstance
    Properties:
      Engine: aurora
      DBClusterIdentifier: !Ref "DatabaseCluster"
      DBInstanceClass: !FindInMap [!Ref "AWS::AccountId", !Ref "AWS::Region", "InstanceType"]
      DBSubnetGroupName: !Ref "DatabaseSubnetGroup"

  DatabasePrimaryCPUAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmDescription: Primary database CPU utilization is over 80%.
      Namespace: AWS/RDS
      MetricName: CPUUtilization
      Unit: Percent
      Statistic: Average
      Period: 300
      EvaluationPeriods: 2
      Threshold: 80
      ComparisonOperator: GreaterThanOrEqualToThreshold
      Dimensions:
        - Name: DBInstanceIdentifier
          Value: !Ref "DatabasePrimaryInstance"
      AlarmActions:
        - Ref: StackAlarmTopic
      InsufficientDataActions:
        - Ref: StackAlarmTopic

  DatabasePrimaryMemoryAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmDescription: Primary database freeable memory is under 700MB.
      Namespace: AWS/RDS
      MetricName: FreeableMemory
      Unit: Bytes
      Statistic: Average
      Period: 300
      EvaluationPeriods: 2
      Threshold: 700000000
      ComparisonOperator: LessThanOrEqualToThreshold
      Dimensions:
        - Name: DBInstanceIdentifier
          Value: !Ref "DatabasePrimaryInstance"
      AlarmActions:
        - Ref: StackAlarmTopic
      InsufficientDataActions:
        - Ref: StackAlarmTopic

  DatabasePrimaryReplicationAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmDescription: Database replication latency is over 200ms.
      Namespace: AWS/RDS
      MetricName: AuroraReplicaLag
      Unit: Milliseconds
      Statistic: Average
      Period: 300
      EvaluationPeriods: 2
      Threshold: 200
      ComparisonOperator: GreaterThanOrEqualToThreshold
      Dimensions:
        - Name: DBInstanceIdentifier
          Value: !Ref "DatabaseReplicaInstance"
      AlarmActions:
        - Ref: StackAlarmTopic

  DatabaseReplicaInstance:
    Type: AWS::RDS::DBInstance
    Properties:
      Engine: aurora
      DBClusterIdentifier: !Ref "DatabaseCluster"
      DBInstanceClass: !FindInMap [!Ref "AWS::AccountId", !Ref "AWS::Region", "InstanceType"]
      DBSubnetGroupName: !Ref "DatabaseSubnetGroup"

  DatabaseReplicaCPUAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmDescription: Replica database CPU utilization is over 80%.
      Namespace: AWS/RDS
      MetricName: CPUUtilization
      Unit: Percent
      Statistic: Average
      Period: 300
      EvaluationPeriods: 2
      Threshold: 80
      ComparisonOperator: GreaterThanOrEqualToThreshold
      Dimensions:
        - Name: DBInstanceIdentifier
          Value: !Ref "DatabaseReplicaInstance"
      AlarmActions:
        - Ref: StackAlarmTopic
      InsufficientDataActions:
        - Ref: StackAlarmTopic

  DatabaseReplicaMemoryAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmDescription: Replica database freeable memory is under 700MB.
      Namespace: AWS/RDS
      MetricName: FreeableMemory
      Unit: Bytes
      Statistic: Average
      Period: 300
      EvaluationPeriods: 2
      Threshold: 700000000
      ComparisonOperator: LessThanOrEqualToThreshold
      Dimensions:
        - Name: DBInstanceIdentifier
          Value: !Ref "DatabaseReplicaInstance"
      AlarmActions:
        - Ref: StackAlarmTopic
      InsufficientDataActions:
        - Ref: StackAlarmTopic

  DatabaseReplicaReplicationAlarm:
    Type: AWS::CloudWatch::Alarm
    Properties:
      AlarmDescription: Database replication latency is over 200ms.
      Namespace: AWS/RDS
      MetricName: AuroraReplicaLag
      Unit: Milliseconds
      Statistic: Average
      Period: 300
      EvaluationPeriods: 2
      Threshold: 200
      ComparisonOperator: GreaterThanOrEqualToThreshold
      Dimensions:
        - Name: DBInstanceIdentifier
          Value: !Ref "DatabaseReplicaInstance"
      AlarmActions:
        - Ref: StackAlarmTopic

@Venkatachandu0225,

You should explicitly set the Port property to 5432 in your cloud formation template for the cluster resource. When the engine mode is provisioned it will default to 3306 for both MySQL and Postgre:

https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-rds-dbcluster.html#cfn-rds-dbcluster-port