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Difficulty: MediumManaging Technology Debt and Legacy Cloud Migrations

An enterprise insurance provider is migrating its legacy claims processing platform to Google Cloud to reduce technical debt. The system consists of stateless application services connected to an on-premises relational database. The project team plans to implement a blue-green deployment pattern in Google Cloud to release new cloud-native microservices while updating the underlying database schema. Business continuity policies mandate zero downtime and immediate rollback capabilities if the new release fails. Which architecture strategy should the Cloud Architect recommend to manage database changes during this legacy migration phase?

  1. Adopt an expand-and-contract database schema migration pattern to ensure backward compatibility for the active blue deployment while supporting the new green release.Answer
  2. B
    Apply non-backward-compatible database schema migrations directly to the live database prior to routing traffic to the green deployment environment.
  3. C
    Migrate the database workload directly to Cloud Spanner to automatically handle database schema modifications without requiring application-level schema compatibility logic.
  4. D
    Deploy a multi-region Google Kubernetes Engine cluster to automatically intercept and transform incompatible database queries at the network proxy layer.

Answer

Adopt an expand-and-contract database schema migration pattern to ensure backward compatibility for the active blue deployment while supporting the new green release.
The correct strategy is to adopt an expand-and-contract (parallel change) database schema migration pattern. When executing a blue-green deployment, both the old application version (blue) and the new application version (green) may run concurrently against the database. Using an expand-and-contract strategy ensures all schema changes are additive and backward-compatible during the transition phase, allowing the legacy blue application to remain functional and enabling instant rollback if issues occur with the green version.

Step-by-Step Solution

1
Analyze the zero-downtime and rollback requirements for blue-green application releases during cloud migration.
Identified that both the old (blue) and new (green) application versions must be capable of interacting with the shared database concurrently during traffic cutover.
If schema changes break the blue environment, instant rollback becomes impossible.
2
Evaluate database schema refactoring patterns suitable for legacy cloud migrations.
Determined that the expand-and-contract pattern (adding new columns/tables without removing old ones) supports backward compatibility.
This allows the legacy application to function normally while the upgraded green version utilizes the new schema.
3
Finalize the schema evolution plan for post-migration technical debt remediation.
Plan to contract (remove deprecated columns/tables) only after the green version is fully stabilized and the blue environment is decommissioned.
This completes the technical debt cleanup safely without service interruption.

Key Concept

Expand-and-contract (parallel change) pattern for database schema migrations in zero-downtime deployments
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Topics

Managing Technology Debt and Legacy Cloud Migrations

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