The correct choice is to add a second cluster in a different zone within the same region and enable multi-cluster routing to automatically failover. This configuration achieves Cloud Bigtable high availability because synchronous replication between clusters within a region guarantees a Recovery Point Objective of zero—no data loss—while multi-cluster routing automatically directs traffic to the healthy cluster, meeting the Recovery Time Objective of under five minutes during a zone outage. On the Google Professional Cloud Developer exam, this scenario tests your understanding of regional replication versus multi-region replication; a common trap is assuming you need clusters in different regions, which introduces asynchronous replication and potential data loss. Remember that for zero data loss and fast failover, keep clusters within the same region and use multi-cluster routing. A useful memory tip: “Same region, sync replication, zero RPO; different region, async replication, possible RPO.”
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. 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.
A large e-commerce platform uses Cloud Bigtable to store user session data and product recommendations. They have a single cluster in a single zone. During a recent zone outage, the application became unavailable for 30 minutes because Cloud Bigtable was unreachable. The team needs to ensure high availability for the session data with a Recovery Time Objective (RTO) of less than 5 minutes and a Recovery Point Objective (RPO) of zero (no data loss). What should they do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a second cluster in a different zone within the same region and use multi-cluster routing to automatically failover.
Option B is correct because adding a second Cloud Bigtable cluster in a different zone within the same region and enabling multi-cluster routing provides automatic failover with an RTO of under 5 minutes and an RPO of zero. Multi-cluster routing directs read and write requests to the nearest healthy cluster, and replication between clusters is synchronous within a region, ensuring no data loss during a zone outage.
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.
✗
Migrate the session data to Cloud Memorystore for Redis with persistence and replication.
Why it's wrong here
Redis replication is asynchronous and may lose data; migration is complex.
✓
Add a second cluster in a different zone within the same region and use multi-cluster routing to automatically failover.
Why this is correct
Multi-cluster within region provides zone-level HA with fast replication.
Related concept
Read the scenario before looking for a memorised answer.
✗
Configure replication to a second cluster in a different region and use global routing to failover.
Why it's wrong here
Cross-region replication adds latency and may not achieve RPO zero due to eventual consistency.
✗
Use Cloud Bigtable's single-cluster replication to a different zone.
Why it's wrong here
Single-cluster replication is not a supported configuration.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that cross-region replication can achieve an RPO of zero, but candidates must remember that only intra-region replication is synchronous, while cross-region replication is asynchronous and introduces data loss risk.
Detailed technical explanation
How to think about this question
Cloud Bigtable's replication within a region uses synchronous replication to ensure strong consistency and zero data loss, while multi-cluster routing uses a routing policy that automatically redirects requests to an available cluster based on health checks and latency. Under the hood, each cluster maintains its own set of tablets, and replication streams are applied in near real-time, with failover typically completing in seconds. In a real-world scenario, this setup allows the e-commerce platform to continue serving session data and product recommendations without interruption during a zone failure, meeting strict RTO and RPO requirements.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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: Add a second cluster in a different zone within the same region and use multi-cluster routing to automatically failover. — Option B is correct because adding a second Cloud Bigtable cluster in a different zone within the same region and enabling multi-cluster routing provides automatic failover with an RTO of under 5 minutes and an RPO of zero. Multi-cluster routing directs read and write requests to the nearest healthy cluster, and replication between clusters is synchronous within a region, ensuring no data loss during a zone outage.
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.
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Question Discussion
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