aws cloudformation里rds只读副本怎么写

[gqd12138]

是这样的，我用cloudformation建数据库和只读副本的时候，因为这两个之间有主从关系，必须先建了rds后才能在建只读副本，但是他执行代码的时候不会管这个的，会报错误，所以我cloudformation里应该怎么写，是不是有什么代码会让这两个在建的时候，让只读副本等待rds完成后再建立

[arcane8964]

https://github.com/awslabs/aws-cloudformation-templates/blob/master/aws/services/RDS/RDS_MySQL_With_Read_Replica.yaml#L89-L113

  MasterDB:
    Type: AWS::RDS::DBInstance
    Properties:
      DBName: !Ref 'DBName'
      AllocatedStorage: !Ref 'DBAllocatedStorage'
      DBInstanceClass: !Ref 'DBInstanceClass'
      Engine: MySQL
      MasterUsername: !Ref 'DBUser'
      MasterUserPassword: !Ref 'DBPassword'
      MultiAZ: !Ref 'MultiAZ'
      Tags:
      - Key: Name
        Value: Master Database
      VPCSecurityGroups: !If [Is-EC2-VPC, [!GetAtt [DBEC2SecurityGroup, GroupId]],
        !Ref 'AWS::NoValue']
      DBSecurityGroups: !If [Is-EC2-Classic, [!Ref 'DBSecurityGroup'], !Ref 'AWS::NoValue']
    DeletionPolicy: Snapshot
  ReplicaDB:
    Type: AWS::RDS::DBInstance
    Properties:
      SourceDBInstanceIdentifier: !Ref 'MasterDB'
      DBInstanceClass: !Ref 'DBInstanceClass'
      Tags:
      - Key: Name
        Value: Read Replica Database

用 “SourceDBInstanceIdentifier”， AWS 会自动解决dependency.