Is it possible to Clone an Existing MYSQL Slave Database into Amazon RDS with the RDS clone being a slave to an external Master?
This is completely possible. The only type of import you can use with RDS is a logical restore, so mysqldump. You will want to use the --dump-slave=2 option :

mysqldump --dump-slave=2 (other options) &gt; dump.sql


This will add the CHANGE MASTER statement as a SQL comment to the dump.sql file. Take the binary log file and log position from that statement and set the RDS up accordingly:

CALL mysql.rds_set_external_master (
  host_name
  , host_port
  , replication_user_name
  , replication_user_password
  , &lt;binary log file&gt;
  , &lt;binary log position&gt;
);


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I would caution you that your replication events are going to be sent as plain text, since ssl_encryption is not implemented for RDS MySQL. If your existing master is not in AWS, to be secure you would need to have your RDS instance in a VPC and set up to communicate with a VPN in your existing infrastructure. Read more about this in the docs: https://aws.amazon.com/vpc/