You get an error when you try to register an Oracle RDS database. Or, a registered Oracle RDS instance monitor shuts down. The error may look something like this:
Monitor for database [DATABASENAME] failed in job [QuickPollJob] due to [could not connect to monitored database]. Will attempt to retry every  seconds...org.quartz.JobExecutionException: QuickPollJob failed [See nested exception: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: IO Error: Got minus one from a read call]
Other possible errors include:
ORA-12516, TNS:listener could not find available handler with matching protocol stack
ORA-12519, TNS:listener could not hand off client connection
The Oracle database has hit the process limit and needs more processes.
Increase the process limit of the monitored database. If the Oracle database uses the SPFILE for configuration, you can edit the file to increase the limit. Example:
alter system set processes = 200 scope=spfile;