AZ-900 Describe Azure architecture and services Practice Question
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?
⚠ Common exam trap
Many exam-takers 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.
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
✓
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.
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
Azure SQL Database is a relational database service that stores data on disk, so while it can persist session state, each query involves network I/O, disk access, and SQL processing overhead, making typical latency in the low milliseconds rather than sub-millisecond. Even with premium tiers and in-memory OLTP, it is not designed for the ultra-low latency access pattern required for scaling out session state. The overhead of connection management and the TDS protocol further adds to the delay, making it a valid but non-optimal choice.
- ✗
Azure Blob Storage
Why it's wrong here
Azure Blob Storage is an object storage service for large unstructured data like files, images, and videos, not for frequent small reads and writes. Each access is an HTTP REST call to a distributed system, causing latency that usually ranges from tens to hundreds of milliseconds. Furthermore, blobs are immutable in practice (you overwrite the entire blob), which is inefficient for updating session state that changes on every interaction.
- ✓
Azure Cache for Redis
Why this is correct
Azure Cache for Redis is a managed implementation of the open-source Redis, which stores all data in memory, guaranteeing sub-millisecond read and write operations. It provides native session state support through operations like SET with expiration, and its distributed architecture allows multiple application instances to share the same session data consistently. With features like replication, persistence, and failover, it is specifically designed for high-performance scenarios like web session state, making it the correct choice.
- ✗
Azure Table Storage
Why it's wrong here
Azure Table Storage is a NoSQL key-value store that offers scalable, schema-less data storage, but it is disk-based and accessed via REST endpoints, resulting in latency typically in the 10-50 millisecond range. It also lacks built-in automatic expiration like session state commonly requires, and its simple key-value model lacks the rich data structures (e.g., hashes, lists) that make Redis efficient for session management. For these reasons, it cannot match the sub-millisecond performance of an in-memory cache.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This AZ-900 practice question is part of Courseiva's free Microsoft 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 AZ-900 exam.