- A
A Compute Engine instance group with managed instance groups and a regional persistent disk configured for synchronous replication.
Regional persistent disks replicate data synchronously across zones, and the managed instance group can automatically fail over to a new instance in another zone on failure, achieving high availability.
- B
Use Cloud SQL with automatic failover and read replicas.
Why wrong: Cloud SQL is a managed service; the question specifies running the database on Compute Engine, implying the team wants to manage the database themselves.
- C
Two Compute Engine instances in different zones with a shared Zonal persistent disk.
Why wrong: Zonal persistent disks cannot be attached to instances in different zones simultaneously. This configuration is not supported.
- D
Single Compute Engine instance with a persistent disk snapshot scheduled every hour.
Why wrong: Snapshots provide point-in-time recovery but do not ensure high availability. Recovery time can be hours, failing the 99.99% availability target.
Quick Answer
The answer is a Compute Engine instance group with managed instance groups and a regional persistent disk configured for synchronous replication. This architecture achieves 99.99% availability for a stateful database by running the database across two zones while the regional persistent disk synchronously writes every data block to both zones, ensuring zero data loss during a zone failure. On the Google Professional Cloud Developer exam, this scenario tests your understanding of how to combine zonal redundancy with stateful workloads, often appearing as a trap where candidates mistakenly choose a snapshot-based or backup-only solution that cannot meet the 99.99% uptime requirement. The key distinction is that regional persistent disks provide synchronous replication at the block level, unlike asynchronous replication or manual failover. Remember the mnemonic “MIG with RPD” — Managed Instance Group plus Regional Persistent Disk equals synchronous, zone-fault-tolerant high availability.
PCD Practice Question: Designing highly scalable, available, and reliable cloud-native applications
This PCD practice question tests your understanding of designing highly scalable, available, and reliable cloud-native applications. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
A company runs a critical application on Compute Engine with a stateful database. They need to achieve 99.99% availability for the database tier. Which architecture should they implement?
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
A Compute Engine instance group with managed instance groups and a regional persistent disk configured for synchronous replication.
Option A is correct because a managed instance group with a regional persistent disk configured for synchronous replication provides the necessary 99.99% availability by ensuring the database runs across two zones with synchronous writes to both replicas. This architecture allows automatic failover within seconds if one zone fails, meeting the high-availability requirement without data loss.
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.
- ✓
A Compute Engine instance group with managed instance groups and a regional persistent disk configured for synchronous replication.
Why this is correct
Regional persistent disks replicate data synchronously across zones, and the managed instance group can automatically fail over to a new instance in another zone on failure, achieving high availability.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use Cloud SQL with automatic failover and read replicas.
Why it's wrong here
Cloud SQL is a managed service; the question specifies running the database on Compute Engine, implying the team wants to manage the database themselves.
- ✗
Two Compute Engine instances in different zones with a shared Zonal persistent disk.
Why it's wrong here
Zonal persistent disks cannot be attached to instances in different zones simultaneously. This configuration is not supported.
- ✗
Single Compute Engine instance with a persistent disk snapshot scheduled every hour.
Why it's wrong here
Snapshots provide point-in-time recovery but do not ensure high availability. Recovery time can be hours, failing the 99.99% availability target.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a shared zonal persistent disk across two instances provides high availability, but the trap is that a zonal disk is still tied to a single zone and fails if that zone goes down, whereas a regional persistent disk is required for true multi-zone resilience.
Detailed technical explanation
How to think about this question
Regional persistent disks use synchronous replication at the block level, meaning every write is committed to both zones before acknowledging the write to the application, ensuring zero data loss (RPO=0) during a zonal failure. The managed instance group uses a health check to detect instance failure and automatically launches a new instance in the surviving zone, attaching the regional disk, achieving a recovery time objective (RTO) typically under 60 seconds. This architecture is ideal for stateful databases like Cassandra or MySQL with replication, but requires careful configuration of the database to handle the shared disk (e.g., using a distributed lock manager or active-passive setup).
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this PCD question test?
Designing highly scalable, available, and reliable cloud-native applications — This question tests Designing highly scalable, available, and reliable cloud-native applications — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: A Compute Engine instance group with managed instance groups and a regional persistent disk configured for synchronous replication. — Option A is correct because a managed instance group with a regional persistent disk configured for synchronous replication provides the necessary 99.99% availability by ensuring the database runs across two zones with synchronous writes to both replicas. This architecture allows automatic failover within seconds if one zone fails, meeting the high-availability requirement without data loss.
What should I do if I get this PCD question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
2 more ways this is tested on PCD
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company runs a stateful application on Compute Engine instances with persistent disks. The application must be highly available and be able to recover from a zonal failure with minimal data loss. The current architecture uses a single instance in one zone. Which design should the team implement?
medium- A.Use a standard persistent disk and configure a global load balancer to failover.
- B.Create a snapshot schedule and restore the snapshot to a new instance in another zone on failure.
- ✓ C.Use a regional persistent disk attached to a managed instance group across two zones.
- D.Migrate to Cloud Filestore for shared file storage across zones.
Why C: Option C is correct because a regional persistent disk synchronously replicates data across two zones, and when attached to a managed instance group (MIG) spanning those zones, it provides automatic failover with minimal data loss. This design ensures that if one zone fails, the MIG can detach the disk from the failed instance and attach it to a healthy instance in the surviving zone, preserving state with near-zero RPO.
Variation 2. A company runs a stateful application on Compute Engine with regional persistent disks. They want to achieve high availability with automatic failover in case of a zone failure. Which architecture meets these requirements?
hard- A.Use Cloud Storage FUSE to mount a multi-regional bucket as a filesystem
- B.Use standard persistent disks with scheduled snapshots to a multi-region bucket
- C.Use zonal persistent disks with a managed instance group in a single zone
- ✓ D.Use regional persistent disks with a managed instance group spanning two zones
Why D: Option D is correct because regional persistent disks synchronously replicate data across two zones, and when combined with a managed instance group (MIG) spanning those same two zones, the application can automatically fail over to the healthy zone if one zone fails. The MIG's autohealing and health-check mechanisms detect the failure and recreate instances in the surviving zone, while the regional PD remains accessible from either zone, ensuring high availability without manual intervention.
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Last reviewed: Jun 25, 2026
This PCD practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCD exam.
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