Não consigo conectar no RDS

Tanto via aplicação no TomCat quanto via SQL Client (HeidiSQL)

Segue alguns prints das configurações: Connectivity & security - 1.1 Connectivity & security - 1.2 Configuration

Deve ser alguma configuração de segurança que foi adicionada pela amazon em versão posterior a utilizada na gravação do curso, pois tive problemas de acesso semelhantes para usar o S3.

Na aplicação recebo essas mensagens no log:

Erro genérico acontecendo
org.springframework.transaction.CannotCreateTransactionException: Could not open JPA EntityManager for transaction; nested exception is javax.persistence.PersistenceException: org.hibernate.exception.JDBCConnectionException: Could not open connection
    at org.springframework.orm.jpa.JpaTransactionManager.doBegin(JpaTransactionManager.java:430)
    at org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:373)
...
Caused by: javax.persistence.PersistenceException: org.hibernate.exception.JDBCConnectionException: Could not open connection
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1763)
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1677)
...
Caused by: org.hibernate.exception.JDBCConnectionException: Could not open connection
    at org.hibernate.exception.internal.SQLStateConversionDelegate.convert(SQLStateConversionDelegate.java:132)
    at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:49)
...
Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
...
Caused by: java.net.ConnectException: Connection timed out: connect
    at java.base/java.net.PlainSocketImpl.connect0(Native Method)
    at java.base/java.net.PlainSocketImpl.socketConnect(PlainSocketImpl.java:101)

e no Client SQL mesma coisa:

Can't connect to MySQL server on 'db-casadocodigo.xxxxxxxxxxxx.us-east-1.rds.amazonaws.com'
(10060)

Vou continuar pesquisando, mas espero que alguém consiga me ajudar, pois sem passar dessa parte, não consigo continuar o curso :(

Agradeço desde já ;)