Azure Cosmos DB is the correct choice because it is a globally distributed, multi-master database service that guarantees less than 10 milliseconds latency for reads and writes regardless of geographic location. This low latency is achieved through its turnkey global distribution and multi-master replication, which allows any Azure region to accept writes and automatically replicate data across the globe, ensuring consistent single-digit millisecond performance at any scale. On the AZ-900 exam, this question tests your understanding of which Azure service solves specific workload requirements—here, the key differentiators are “globally distributed,” “multi-master,” and “sub-10 ms latency,” which are unique to Cosmos DB. A common trap is confusing Cosmos DB with Azure SQL Database or Azure Database for PostgreSQL, which do not offer native multi-master writes or guaranteed low latency across regions. To remember this, think of “Cosmos” as “Cosmic scale”—it spans the globe with fast writes everywhere, unlike regional databases that are tied to one location.
AZ-900 Describe Azure architecture and services Practice Question
This AZ-900 practice question tests your understanding of describe azure architecture and services. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 needs a globally distributed, multi-master database that guarantees less than 10 milliseconds latency for reads and writes regardless of geographic location. Which Azure service should they use?
Why wrong: Azure SQL Database with geo-replication has a secondary read replica — it doesn't support multi-master writes or guarantee sub-10ms global latency.
B
Azure Cosmos DB
Cosmos DB provides global distribution with multi-region writes and guarantees single-digit millisecond latency worldwide.
C
Azure Cache for Redis
Why wrong: Redis provides low latency but is a caching layer, not a persistent globally distributed multi-master database.
D
Azure Database for PostgreSQL with read replicas
Why wrong: Read replicas provide geographic read distribution but don't support multi-master writes.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Azure Cosmos DB
Azure Cosmos DB is the correct choice because it is a globally distributed, multi-master database service that offers turnkey global distribution, single-digit millisecond latency (less than 10 ms) for both reads and writes at any scale, and supports multiple consistency models. Its multi-master capability allows any region to accept writes, which is essential for the stated requirement of low-latency writes regardless of geographic location.
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.
✗
Azure SQL Database with geo-replication
Why it's wrong here
Azure SQL Database with geo-replication has a secondary read replica — it doesn't support multi-master writes or guarantee sub-10ms global latency.
✓
Azure Cosmos DB
Why this is correct
Cosmos DB provides global distribution with multi-region writes and guarantees single-digit millisecond latency worldwide.
Related concept
Read the scenario before looking for a memorised answer.
✗
Azure Cache for Redis
Why it's wrong here
Redis provides low latency but is a caching layer, not a persistent globally distributed multi-master database.
✗
Azure Database for PostgreSQL with read replicas
Why it's wrong here
Read replicas provide geographic read distribution but don't support multi-master writes.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse geo-replication (which provides read-only secondaries) with true multi-master global distribution, leading them to select Azure SQL Database with geo-replication when the requirement explicitly demands multi-master writes with guaranteed low latency.
Detailed technical explanation
How to think about this question
Azure Cosmos DB achieves this by replicating data across any number of Azure regions using a multi-master replication protocol that supports multiple write regions simultaneously, with automatic conflict resolution via last-writer-wins (LWW) or custom conflict resolution policies. The service exposes data through multiple APIs (SQL, MongoDB, Cassandra, Gremlin, Table) and allows tuning consistency from strong to eventual, with the default session consistency providing balanced performance. In a real-world scenario, a global e-commerce platform can use Cosmos DB to allow users in different continents to write to their local region without cross-region write latency, while still maintaining global data consistency as needed.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this AZ-900 question in full detail.
Describe Azure architecture and services — This question tests Describe Azure architecture and services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Azure Cosmos DB — Azure Cosmos DB is the correct choice because it is a globally distributed, multi-master database service that offers turnkey global distribution, single-digit millisecond latency (less than 10 ms) for both reads and writes at any scale, and supports multiple consistency models. Its multi-master capability allows any region to accept writes, which is essential for the stated requirement of low-latency writes regardless of geographic location.
What should I do if I get this AZ-900 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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