The correct answer is to use Cloud Spanner for global application strong consistency writes with Cloud CDN for reads. This works because Cloud Spanner leverages TrueTime and Paxos-based synchronous replication to guarantee strong consistency across regions for every write, while Cloud CDN serves stale-but-acceptable read data from edge caches, perfectly matching the requirement for eventual consistency on reads. On the Google Professional Cloud Developer exam, this scenario tests your understanding that Spanner is the only globally distributed database offering external consistency, and the common trap is assuming you need Spanner for reads too—remember, CDN handles read-heavy traffic efficiently. A useful memory tip: “Spanner for the pen, CDN for the lens”—writes must be strongly consistent, but reads can tolerate a slightly outdated view.
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 team is designing a globally distributed application on Google Cloud that requires strong consistency for writes but can tolerate eventual consistency for reads. The application expects millions of concurrent users. Which two strategies should they implement? (Choose two.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use Cloud Spanner for write operations requiring strong consistency.
Cloud Spanner provides strongly consistent writes globally through synchronous replication using the TrueTime API and Paxos-based consensus. This ensures that all write operations are immediately consistent across regions, meeting the requirement for strong consistency on writes.
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.
✓
Use Cloud Spanner for write operations requiring strong consistency.
Why this is correct
Spanner provides global strong consistency and high availability.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use Firestore in multi-region mode for all operations.
Why it's wrong here
Firestore multi-region provides strong consistency but not optimized for global writes with low latency.
✓
Use global HTTP(S) Load Balancer with Cloud CDN for read-heavy traffic.
Read the scenario before looking for a memorised answer.
✗
Deploy Cloud SQL with cross-region replication for read scalability.
Why it's wrong here
Cross-region replication is asynchronous, leading to eventual consistency.
✗
Use Cloud Bigtable for reading data with strong consistency.
Why it's wrong here
Bigtable does not provide strong consistency for reads.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a single database can handle both strong consistency and high scalability for reads and writes, leading candidates to choose Firestore or Bigtable without considering the specific consistency requirements for writes versus reads.
Detailed technical explanation
How to think about this question
Cloud Spanner uses TrueTime, a globally synchronized clock, to assign commit timestamps that guarantee external consistency (linearizability) for writes. This is achieved through a two-phase commit protocol with Paxos groups, ensuring that all replicas agree on the order of transactions. In contrast, Cloud CDN caches static or dynamic content at edge locations, reducing read latency for globally distributed users, but it does not affect write consistency; the load balancer distributes traffic to the nearest healthy backend, which can be Spanner instances.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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: Use Cloud Spanner for write operations requiring strong consistency. — Cloud Spanner provides strongly consistent writes globally through synchronous replication using the TrueTime API and Paxos-based consensus. This ensures that all write operations are immediately consistent across regions, meeting the requirement for strong consistency on writes.
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 →
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 multi-region application uses Cloud Spanner. The team needs to ensure that a write is immediately visible to all subsequent reads, even those performed in different regions. Which consistency mode should they use?
hard
A.Eventual consistency
B.Global consistency
C.Bounded staleness
✓ D.Strong consistency
Why D: Strong consistency (D) ensures that once a write is acknowledged, any subsequent read, regardless of region, will reflect that write. Cloud Spanner uses the TrueTime API and Paxos-based replication to provide external consistency (a form of strong consistency) across regions, making it the correct choice for immediate global visibility.
Last reviewed: Jun 11, 2026
Question Discussion
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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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