GCP PCA Drill: Database Migration Strategy - The Cutover Trade-off

While preparing for the GCP Professional Cloud Architect (PCA) exam, many candidates struggle with database migration and cutover strategies. In the real world, this is fundamentally a decision about balancing minimal downtime with operational simplicity and reliability. Let’s drill into a simulated scenario.

The Architecture Drill (Simulated Question)

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Scenario

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A global online gaming startup, PixelForge Games, is migrating a critical part of their user profile service from an on-premises MySQL database to Google Cloud. The application runs on Compute Engine VMs and relies heavily on the MySQL database for low-latency reads and writes. PixelForge wants to migrate their database to Cloud SQL with near-zero downtime and no data loss to maintain player experience during the transition. The development team also wants to minimize application changes. The key challenge is determining the optimal cutover strategy between the on-premises environment and Google Cloud.

The Requirement:

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Perform the migration of their MySQL-backed application to Google Cloud using Compute Engine and Cloud SQL with:

• Minimal downtime (near zero)
• No data loss
• Minimal modifications to application code
• Secure and reliable access during migration

The Options

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• A)

  1. Set up Cloud VPN to provide private network connectivity between Compute Engine and on-prem MySQL.
  2. Stop the on-premises application.
  3. Create a mysqldump from the on-premises MySQL.
  4. Upload the dump to Cloud Storage.
  5. Import the dump into Cloud SQL.
  6. Modify the application source code to write queries to both databases (on-prem and Cloud SQL) and read from the local database.
  7. Start the Compute Engine application.
  8. Stop the on-premises application.

• B)

  1. Set up Cloud SQL Proxy and MySQL Proxy.
  2. Create a mysqldump from on-premises MySQL.
  3. Upload the dump to Cloud Storage.
  4. Import the dump into Cloud SQL.
  5. Stop the on-premises application.
  6. Start the Compute Engine application.

• C)

  1. Set up Cloud VPN to create private network connectivity between Compute Engine and on-prem MySQL.
  2. Stop the on-premises application.
  3. Start the Compute Engine application configured to read and write to the on-premises MySQL server.
  4. Create a replication configuration in Cloud SQL.
  5. Configure the on-prem MySQL server to accept connections from the Cloud SQL replica.
  6. Finalize the Cloud SQL replica configuration.
  7. When replication completes, stop the Compute Engine application.
  8. Promote the Cloud SQL replica to a standalone instance.
  9. Restart the Compute Engine application configured to read and write to Cloud SQL standalone instance.

• D)

  1. Stop the on-premises application.
  2. Create a mysqldump of the on-premises MySQL server.
  3. Upload the dump to Cloud Storage.
  4. Import the dump into Cloud SQL.
  5. Start the application on Compute Engine.

Correct Answer

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Option C

The Architect’s Analysis

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Correct Answer

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Option C

The Winning Logic

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Option C leverages Cloud SQL’s native replication features to set up asynchronous replication from the on-premises MySQL instance to Cloud SQL. This approach:

• Enables continuous data sync, eliminating data loss risk during the migration window
• Minimizes downtime by allowing application reads/writes during replication
• Avoids complex dual writes or manual merging by delegating sync responsibility to Cloud SQL replication
• Allows a clean cutover by promoting the Cloud SQL replica to primary once sync is complete
• Uses private VPN connectivity to secure cross-environment traffic
• Requires minimal application modification — only reconfigure the database endpoint post cutover

This adheres to the SRE principle of reducing operational toil by leveraging managed services’ replication capabilities instead of custom sync logic. It also aligns with FinOps best practices by minimizing prolonged dual-write complexity and prevents costly outages with minimal downtime.

The Trap (Distractor Analysis):

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• Why not A?

  • Dual writes require code changes, increase data inconsistency risk, and create operational toil.
  • Stopping app twice increases downtime windows.

• Why not B?

  • Cloud SQL Proxy helps connectivity, but stopping the app before migration causes downtime.
  • No replication means data could be stale or lost during migration.

• Why not D?

  • Downtime can be long as the dump-import process is manual and offline, risking lost data changes during migration window.
  • Simplistic approach doesn’t satisfy near-zero downtime requirement.

The Architect Blueprint

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• Mermaid Diagram illustrating the flow of the CORRECT solution.

• Diagram Note: The app initially reads/writes on-prem MySQL over VPN during replication. After replica promotion, traffic shifts seamlessly to Cloud SQL standalone.

The Decision Matrix

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Real-World Application (Practitioner Insight)

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Exam Rule

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For the exam, always choose Cloud SQL replication when migrating MySQL workloads requiring minimal downtime and no data loss.

Real World

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Companies often choose Cloud SQL’s native replication in hybrid scenarios to avoid complex manual syncs, reduce operational toil, and accelerate cutovers with confidence.

Disclaimer

This is a study note based on simulated scenarios for the GCP PCA exam. It is not an official question from Google Cloud.