Google PCA Design and plan a cloud solution architecture Practice Question
A company is migrating a monolithic application to Google Cloud. The application consists of a stateful service that writes to local disk and a stateless web server. They want to minimize changes to the code. Which architecture should they use?
⚠ Common exam trap
The trap here is that candidates often over-engineer the solution by choosing cloud-native options (like Cloud Run or GKE) that require code changes, ignoring the explicit requirement to minimize changes and the suitability of a simple lift-and-shift with persistent disks.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Lift and shift to Compute Engine instances with persistent disks for stateful service
It represents a lift-and-shift migration that minimizes code changes by running the monolithic application on Compute Engine instances. The stateful service can use persistent disks for local disk writes, while the stateless web server runs on the same or separate instances, preserving the existing architecture without refactoring.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Run the entire application on Cloud Run and use Cloud Filestore for shared state
Why it's wrong here
Cloud Run is stateless and cannot persist local disk writes; Filestore does not satisfy the stateful service's local-disk dependency without code changes. It tempts because Cloud Run and Filestore are managed and low-effort, but the stem's local-disk writes demand a lift-and-shift VM approach instead.
- ✗
Use App Engine Flexible Environment for the web server and Cloud SQL for state
Why it's wrong here
App Engine Flexible runs the web server, but the stateful service still writes to local disk, which is ephemeral and lost on instance restart; Cloud SQL stores relational data, not filesystem state. It is tempting because App Engine Flex handles stateless web tiers well, and Cloud SQL suits structured state in a lift-and-shift scenario.
- ✗
Refactor the application into microservices and deploy on GKE with StatefulSets
Why it's wrong here
Refactoring into microservices with StatefulSets requires substantial code changes, contradicting the minimise-changes requirement. It tempts because StatefulSets genuinely provide stable identities and persistent volumes for stateful workloads, but that benefit only applies after a rewrite, which this migration explicitly seeks to avoid.
- ✓
Lift and shift to Compute Engine instances with persistent disks for stateful service
Why this is correct
Lift and shift preserves the existing monolithic code, satisfying the minimal-change constraint. Compute Engine persistent disks provide durable block storage that survives instance restarts, so the stateful service's local disk writes remain intact without refactoring into Cloud Storage or a managed database.
Go deeper
Related to this question
Learn chapter
Data Migration and Transfer Services
Key term
Service
A service is a software component or system that performs a specific function and is available to be used by other programs or users over a network.
Key term
Compute Engine
Compute Engine is Google Cloud's Infrastructure-as-a-Service (IaaS) offering that lets you create and run virtual machines on Google's infrastructure.
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