title: Failed to deploy `ProxyTargetGroup` for RDS Aurora postgresql
body: <p>I have deployed an Aurora cluster and a db instance (postgresql 11.8) and a proxy as AWS. When I try to add a proxy target group like below code, the deploy takes one hour and timed out in 2 hours. I have attached the screenshot. It works fine if I manually add the target group through AWS console. I wonder what wrong with my configuration?</p>
  <pre><code>ProxyTargetGroup:
      Type: AWS::RDS::DBProxyTargetGroup
      Properties:
        DBProxyName: !Ref DBProxy
        DBClusterIdentifiers: [!Ref AuroraDBCluster]
        TargetGroupName: default
        ConnectionPoolConfigurationInfo:
            MaxConnectionsPercent: 100
            MaxIdleConnectionsPercent: 50
            ConnectionBorrowTimeout: 120
  </code></pre>
  <p><a href="https://i.stack.imgur.com/KfXAk.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/KfXAk.png" alt="enter image description here" /></a></p>
  <pre><code>DBProxy:
      Type: AWS::RDS::DBProxy
      Properties: 
        Auth:
          - {AuthScheme: SECRETS, SecretArn: !Ref DBSecret, IAMAuth: REQUIRED}
        DBProxyName: ${self:provider.stackName}-dbproxy 
        DebugLogging: true
        EngineFamily: POSTGRESQL
        IdleClientTimeout: 30
        RequireTLS: true
        RoleArn: !GetAtt DBProxyRole.Arn
        VpcSecurityGroupIds:
          - !Ref ClusterSecurityGroup
        VpcSubnetIds:
          - !Ref SubnetAPublic
          - !Ref SubnetAPrivate
          - !Ref SubnetBPrivate
          - !Ref SubnetCPrivate
  DBProxyRole:
      Type: AWS::IAM::Role
      Properties:
        RoleName: ${self:provider.stackName}-dbproxyRole
        AssumeRolePolicyDocument:
          Version: '2012-10-17'
          Statement:
            - Effect: Allow
              Principal:
                Service:
                  - rds.amazonaws.com
              Action: sts:AssumeRole
        Policies:
          - PolicyName: ${self:provider.stackName}-dbproxyPolicy
            PolicyDocument:
              Version: '2012-10-17'
              Statement:
                - Effect: Allow
                  Action:
                    - secretsmanager:GetSecretValue
                    - secretsmanager:GetResourcePolicy
                    - secretsmanager:DescribeSecret
                    - secretsmanager:ListSecretVersionIds
                  Resource:
                    - &quot;arn:aws:secretsmanager:${opt:region}:${self:provider.accountId}:secret:${opt:stage}/${self:service.name}/AuroraUserSecret&quot;
  
                - Effect: Allow
                  Action:
                    - kms:*
                  Resource: 'arn:aws:kms:${opt:region}:${self:provider.accountId}:key/*'
  ClusterSecurityGroup:
      Type: AWS::EC2::SecurityGroup
      Properties:
        GroupDescription: Allow traffic to client host
        VpcId:
          Ref: VPC
        SecurityGroupIngress:
          - IpProtocol: -1
            CidrIp: 0.0.0.0/0
        SecurityGroupEgress:
          - IpProtocol: -1
            CidrIp: 0.0.0.0/0
  
  </code></pre>
  <p>When the cloudformation is showing <code>update in progress</code>, I can see that the target group is added and available. But the cloudformation keeps showing <code>in progress</code> until timed out.</p>