We implemented automated Cloud SQL backup encryption key rotation to meet PCI-DSS requirements for our payment processing database. Our compliance mandate required cryptographic key rotation every 90 days with full audit documentation.
The solution uses Cloud SQL Customer-Managed Encryption Keys (CMEK) integrated with Cloud KMS. We configured automatic key rotation at the KMS level, and Cloud SQL automatically uses the latest key version for new backups. Here’s our KMS key configuration:
gcloud kms keys create payments-backup-key \
--keyring=financial-data \
--location=us-central1 \
--purpose=encryption \
--rotation-period=90d
Critically, audit logging for key usage flows to Cloud Logging, providing complete visibility into which key versions encrypted which backups. This has streamlined our quarterly compliance audits significantly. The auditors can now query logs directly to verify rotation compliance.
Cloud KMS maintains all key versions automatically unless you explicitly disable them. When restoring a backup, Cloud SQL uses the specific key version that encrypted that backup. You don’t need to manually track which version to use - it’s embedded in the backup metadata. The critical point is never disabling or destroying old key versions while backups encrypted with them still exist within your retention period.
From a compliance standpoint, this approach is excellent for PCI-DSS and SOC 2. I’d recommend also implementing key version lifecycle policies. Document which key versions are active vs disabled, and create a runbook for emergency key compromise scenarios. Also ensure your disaster recovery procedures include KMS key recovery - we’ve seen organizations successfully rotate keys but fail to include KMS configuration in their DR plans.
Don’t forget about the IAM permissions required for this setup. The Cloud SQL service account needs cloudkms.cryptoKeyEncrypterDecrypter role on your KMS key. Also, ensure you’re monitoring KMS quota usage - high-frequency backup operations can hit API limits. We use Cloud Monitoring to alert on KMS request rates and error rates.
We export Cloud Logging data to BigQuery daily and have created a Data Studio dashboard showing key rotation timeline, backup encryption status by key version, and restore operations. For auditors, we generate PDF reports monthly with summary statistics and detailed logs for any anomalies. The dashboard makes it trivial to answer questions like “show me all backups encrypted with key version X” or “prove rotation occurred on schedule.”