source
The type of source instance. If the source instance is a PolarDB O engine cluster, the source instance type needs to be OTHER or EXPRESS as a self-built database, and access via public IP or dedicated line. For the correspondence between supported source and target instances, see Supported Databases. When the source instance is a self-built database, you also need to perform corresponding preparations, for details, see Preparations Overview. Valid values: CEN, DG, DISTRIBUTED_DMSLOGICDB, ECS, EXPRESS, MONGODB, OTHER, PolarDB, POLARDBX20, RDS.