Incoming connections should use SSL while making connections with Cloud SQL database instances.
Cloud SQL for MySQL is a fully managed database service that makes it easy to set up, maintain, manage and administer your relational MySQL databases on a Cloud Platform. It offers data encryption at rest and in transit and private connectivity with VPC and user-controlled network access with firewall protection. Cloud SQL creates a server certificate automatically when a new instance is created. We recommend enforcing all connections to use SSL/TLS when connecting with the Cloud SQL database instances.