The answer is Azure Cache for Redis, because it is an in-memory data store designed for sub-millisecond retrieval, making it the best Azure service for low-latency session state storage for web servers. Unlike disk-based options, Redis keeps session data in RAM, ensuring multiple web server instances can read and write state consistently under one millisecond, even under heavy load. On the AZ-900 exam, this scenario tests your understanding of when to choose in-memory caching over persistent storage like Azure SQL Database or Blob Storage—a common trap is picking a database service for speed, but Redis is purpose-built for ultra-fast, temporary data. Remember the memory tip: “Redis is rapid—RAM-based, not disk-based,” which ties directly to the exam’s focus on matching services to performance requirements.
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.
An application needs to store session state that can be accessed by multiple web server instances. The state must be retrieved in under 1 millisecond. Which Azure service BEST meets this requirement?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Azure Cache for Redis
Azure Cache for Redis is an in-memory data store that provides extremely low-latency (sub-millisecond) read and write operations, making it ideal for storing session state that must be accessed quickly by multiple web server instances. Unlike disk-based storage services, Redis keeps data in RAM, ensuring consistent retrieval times under 1 millisecond even under load.
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
Why it's wrong here
SQL Database can store session state but disk-based queries take milliseconds — not sub-millisecond latency.
✗
Azure Blob Storage
Why it's wrong here
Blob Storage is object storage — latency is too high for sub-millisecond session state access.
✓
Azure Cache for Redis
Why this is correct
Azure Cache for Redis is an in-memory data store providing sub-millisecond latency — ideal for distributed session state.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Azure Table Storage
Why it's wrong here
Table Storage is a NoSQL key-value store but doesn't provide the sub-millisecond latency of in-memory Redis.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose Azure SQL Database or Azure Table Storage because they associate 'state storage' with databases, overlooking the explicit sub-millisecond latency requirement that only an in-memory cache like Redis can satisfy.
Detailed technical explanation
How to think about this question
Azure Cache for Redis is based on the open-source Redis in-memory data structure store, which uses a single-threaded event loop to achieve predictable sub-millisecond latency for simple GET/SET operations. In a real-world scenario, a web farm using Redis for session state can scale horizontally without requiring sticky sessions, as each web server instance reads and writes session data directly from the shared Redis cache, ensuring consistency and performance.
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.
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 Cache for Redis — Azure Cache for Redis is an in-memory data store that provides extremely low-latency (sub-millisecond) read and write operations, making it ideal for storing session state that must be accessed quickly by multiple web server instances. Unlike disk-based storage services, Redis keeps data in RAM, ensuring consistent retrieval times under 1 millisecond even under load.
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.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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