Q:

How to encrypt my existing RDS Instance using Boto3? 

I want to encrypt my existing rds instance. I am using the Boto Script to modify db instance. 
modified_rds_attributes = rds_conn_boto3.modify_db_instance(
    DBInstanceIdentifier=id,
    StorageEncrypted=True
)

Is it possible to encrypt existing RDS DB Instance? 
If Yes,then how can I acheive the task? 

A:

A non encrypted instance cannot be converted to an encrypted one.  You also cannot create an encrypted instance for a non encrypted snapshot or create an encrypted replica of a non encrypted instance.  
The only way is to dump the old instance to a file and then load that into the new (encrypted) instance

A:

I agree that "A non encrypted instance cannot be converted to an encrypted one."  However , I disagree that there is one way to do the mission.  
Another way is to :

take a snapshot from the unencrypted instance.   
copy the snapshot by specifying a Key Management System (KMS) encryption key
then restore a new encrypted instance from snapshot

__
Reference https://aws.amazon.com/blogs/aws/amazon-rds-update-share-encrypted-snapshots-encrypt-existing-instances/

