The best architecture for migrating a legacy stateful monolithic application to Google Cloud with high availability is to deploy on Compute Engine with a regional persistent disk and use Cloud SQL for PostgreSQL with regional high availability. This combination ensures synchronous replication of the application’s state across zones via the regional persistent disk, while Cloud SQL’s managed PostgreSQL provides automatic failover and low-latency database access, directly addressing the need to minimize downtime during a zonal failure. On the Google Professional Cloud Architect exam, this scenario tests your ability to choose between stateful and stateless migration patterns, often using a trap where candidates select Kubernetes or a single-zone deployment, forgetting that a legacy monolithic app with a stateful database does not benefit from container orchestration complexity. The key insight is that regional persistent disks offer block-level replication without application changes, making them ideal for stateful lift-and-shift migrations. Memory tip: “Regional disk for stateful lift, Cloud SQL for database shift.”
Google PCA Ensure solution and operations reliability Practice Question
This PCA practice question tests your understanding of ensure solution and operations reliability. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
An organization is migrating a legacy monolithic application to Google Cloud. The application currently runs on a single server with an on-premises database. The application is stateful and requires low-latency access to the database. The migration must minimize downtime and ensure high availability. Which architecture should the company adopt?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Deploy on Compute Engine with a regional persistent disk and use Cloud SQL for PostgreSQL with regional high availability.
Option B is correct because it combines Compute Engine with a regional persistent disk for synchronous replication across zones, ensuring high availability with minimal downtime during a zonal failure. Cloud SQL for PostgreSQL with regional high availability provides a managed, low-latency database with automatic failover, meeting the stateful application's need for low-latency access and high availability without the complexity of container orchestration.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Deploy on GKE with StatefulSets and use Cloud Spanner for global consistency.
Why it's wrong here
Overly complex and costly; Cloud Spanner may not provide low-latency if not regionally deployed.
✓
Deploy on Compute Engine with a regional persistent disk and use Cloud SQL for PostgreSQL with regional high availability.
Why this is correct
This provides HA and low-latency access needed for the stateful monolithic app.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Deploy on App Engine Standard Environment and use Cloud Firestore in Datastore mode.
Why it's wrong here
App Engine is stateless and Firestore is NoSQL, not suitable for legacy relational app.
✗
Deploy on Cloud Run and use Cloud SQL with read replicas.
Why it's wrong here
Cloud Run is stateless and not ideal for long-running stateful applications.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often overcomplicate the solution by choosing containerized or serverless options (GKE, Cloud Run, App Engine) without recognizing that a legacy monolithic stateful application with low-latency requirements is best served by a simple, proven VM-based architecture with regional persistent disks and a managed relational database with synchronous replication.
Detailed technical explanation
How to think about this question
Regional persistent disks use synchronous replication between two zones (e.g., us-central1-a and us-central1-b) via Google's internal network, ensuring that writes are committed in both zones before acknowledging the write, which provides an RPO of zero. Cloud SQL for PostgreSQL regional high availability uses a primary and standby instance in different zones with synchronous replication, and automatic failover is triggered by a health-check heartbeat mechanism, typically completing within 60 seconds. This architecture minimizes downtime by avoiding the need to reconfigure application connections manually, as the Cloud SQL proxy or private IP can be used with a DNS CNAME that updates on failover.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this PCA question in full detail.
Ensure solution and operations reliability — This question tests Ensure solution and operations reliability — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Deploy on Compute Engine with a regional persistent disk and use Cloud SQL for PostgreSQL with regional high availability. — Option B is correct because it combines Compute Engine with a regional persistent disk for synchronous replication across zones, ensuring high availability with minimal downtime during a zonal failure. Cloud SQL for PostgreSQL with regional high availability provides a managed, low-latency database with automatic failover, meeting the stateful application's need for low-latency access and high availability without the complexity of container orchestration.
What should I do if I get this PCA question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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