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Difficulty: MediumRelease Management and Deployment Strategies (Blue-Green, Canary, Rolling)

A financial payment platform processes real-time credit transactions on Google Cloud using Compute Engine Managed Instance Groups (MIGs) fronted by an External HTTP(S) Load Balancer. The engineering team is planning a zero-downtime blue-green deployment for a major application revision that includes database schema modifications on Cloud SQL for PostgreSQL. Which TWO architectural and operational steps must the team execute to achieve zero downtime and maintain immediate rollback capabilities? (Select TWO answers.)

  1. Apply backward-compatible database schema changes (expand phase) prior to directing live user traffic to the new green instance group.Answer
  2. B
    Execute destructive database schema column removals concurrently with the load balancer traffic cutover to streamline database migration.
  3. Pre-allocate compute instance capacity and confirm passing backend health checks on the green environment before updating load balancer target pool routing.Answer
  4. D
    Rely on automatic default quota increases during traffic cutover rather than validating regional Compute Engine quotas in advance.

Answer

The platform team must apply backward-compatible database schema changes before shifting traffic and ensure green environment compute capacity and health checks are fully validated prior to load balancer cutover.
In blue-green deployments involving relational databases, zero downtime requires decoupled database and application deployments. Using an expand-contract pattern guarantees that database schema updates remain backward-compatible with the active deployment while preparing for the new code release. Additionally, verifying target pool health and regional compute capacity prior to traffic cutover ensures that the green environment can immediately sustain production load without dropping connections.

Step-by-Step Solution

1
Implement the expand phase of an expand-contract schema strategy on Cloud SQL.
Database additions (such as new columns or tables) are made backwards-compatible so legacy blue and updated green application versions function concurrently.
Prevents database errors when both environments interact with the database during canary or blue-green cutovers.
2
Provision and validate the green Compute Engine Managed Instance Group.
Green MIG instances pass HTTP health checks and regional instance quotas are confirmed.
Guarantees full operational readiness and capacity before user request redirection.
3
Update External HTTP(S) Load Balancer URL maps or target pools to switch traffic to the green MIG.
Traffic cutover completes seamlessly with active blue instances serving remaining active connections until drained.
Achieves zero-downtime release with straightforward rollback by reverting load balancer configuration.

Key Concept

Expand-Contract Database Migration and Health Verification in Blue-Green Deployments
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Topics

Release Management and Deployment Strategies (Blue-Green, Canary, Rolling)