srvctl add service -d db -s billing -r "db3,db4" -P PRECONNECT

service_billing =
  (DESCRIPTION =
    (LOAD_BALANCE=on)
    (FAILOVER=ON)
    (ADDRESS = (PROTOCOL = TCP)(HOST = crs-scan)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = billing)
       (FAILOVER_MODE =
        (TYPE = SELECT)
        (METHOD = PRECONNECT)
        (RETRIES = 1)
        (DELAY = 1)
    )
  )
)