Secure Cloud SQL Migration Connectivity and Access

The scenario requires migrating sensitive data from on-premises to Cloud SQL for PostgreSQL while adhering to Google-recommended security practices. The core challenge is establishing a secure, private connectivity path and enforcing strict access controls.

First, consider the connectivity mechanism. Option B suggests using Private Service Connect (PSC). PSC provides a private, internal IP address for Cloud SQL instances, allowing traffic to flow securely between your on-premises network and Google Cloud without traversing the public internet. This is the recommended approach for hybrid connectivity to ensure data remains within Google's private backbone, minimizing exposure to external threats. In contrast, Option C proposes using an external IP with firewall rules. While firewalls are useful, relying on public IPs increases the attack surface and is generally discouraged for sensitive workloads compared to private connectivity solutions like PSC or Cloud Interconnect.

Second, evaluate access management. Option D recommends setting up IAM roles to restrict access when using an internal IP. Combining internal IPs (via PSC) with robust IAM policies ensures that only authorized service accounts or users can connect to the database. This defense-in-depth strategy aligns with the principle of least privilege. Option A focuses on patching and binary logging, which are maintenance features rather than primary migration security controls. Option E involves Storage Transfer Service with client-side encryption; however, this service is designed for object storage (Cloud Storage), not direct relational database migration to Cloud SQL.

Therefore, the combination of private connectivity via PSC (B) and restricted IAM access (D) constitutes the most secure, Google-recommended practice for this migration scenario.