title: AWS CloudFormation Error: !Join object requires two parameters, (1) a string delimiter and (2) a list of strings to be joined
body: <p>I'm getting an error in CloudFormation using the !Join function:</p>
  <p><strong>Template error: every Fn::Join object requires two parameters, (1) a string delimiter and (2) a list of strings to be joined or a function that returns a list of strings (such as Fn::GetAZs) to be joined.</strong></p>
  <p>My Code:</p>
  <pre><code>  RDSSubnetGroup:
      Type: AWS::RDS::DBSubnetGroup
      Condition: CreationRDS
      Properties:
         DBSubnetGroupDescription: !Ref RDSName
         SubnetIds: !Ref SubnetIds
    
    RDSAuroraServerless:
      Type: AWS::RDS::DBCluster
      Condition: CreationRDS
      Properties:
        Engine: aurora-mysql
        EngineMode: serverless
        EngineVersion: !Ref EngineVersion
        DatabaseName: !Ref RDSName
        MasterUsername: admin
        MasterUserPassword: !Ref MasterUserPassword
        DBClusterIdentifier: !Ref RDSName
        ScalingConfiguration:
          MinCapacity: 1
          MaxCapacity: 2
          SecondsUntilAutoPause: 300
        BackupRetentionPeriod: 7
        DeletionProtection: false
        VpcSecurityGroupIds:
          - !Ref SecurityGroup
        DBSubnetGroupName: !Ref RDSSubnetGroup
  
  Outputs:
    JDBCOutput:
      Condition: CreationRDS
      Value: 
        !Join [ '', [!GetAtt RDSAuroraServerless.Endpoint.Address, /, !Ref RDSName] ]
  </code></pre>
  <p>Can you help me and show me where I'm going wrong?</p>