A VPC peering connection with proper route table entries provides private IP connectivity between EC2 instances in separate VPCs. This keeps database traffic off the public internet and satisfies the private communication requirement. To make the traffic secure in transit, the MySQL instance should use an SSL certificate so the application can establish encrypted database connections. RDS Proxy is not valid because the database is self-hosted on EC2, not Amazon RDS. Allowing a public IP address would violate the private traffic requirement. A network ACL also cannot reference a security group ID, so option E is not a valid control. The correct combination is private VPC-to-VPC routing plus database-level encryption in transit.