If you do not add services to PDBs, and then the Oracle RAC One Node CDB fails over to another node, or you manually relocate the CDB to another node, then by default, all PDBs associated with the CDB that do not have registered services are restarted in MOUNTED state.

PDBs are opened in Read-Write mode after failover, in case of Oracle RAC One Node database, or relocation in case of any Oracle RAC database, only after you have configured the PDBs to have associated services. If you have not associated services to PDBs, then the PDBs remains in MOUNTED state when the CDB instance restarts.

To add services to a PDB, use the following srvctl command syntax, where cdbname is the name of the CDB, service_name is the name of the service, and pdbname is the name of the PDB:

srvctl add service -d cdbname -s service_name -pdb pdbname

After you add services to your PDBs, if you relocate the CDB with which the PDBs are associated, or the CDB fails over for Oracle RAC One Node databases, then the PDBs associated with that CDB automatically open in Read-Write state.