AZ-305 Design data storage solutions Practice Question
You are designing a storage solution for a global e-commerce platform that must serve users from multiple regions with low latency. The data includes product catalog (read-heavy, rarely updated) and user session state (write-heavy, short-lived). Which combination of Azure services meets the requirements?
⚠ Common exam trap
It's easy for candidates to confuse Azure Cache for Redis as a durable session store, but it is a volatile cache that requires a persistence strategy (e.g., Redis persistence or Azure Cache for Redis with data persistence) to avoid data loss, which is not suitable for session state that must survive restarts.
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 Cosmos DB for session state and Azure Front Door with Azure CDN for catalog.
Azure Cosmos DB is ideal for session state because it offers multi-region writes with single-digit-millisecond latency and automatic failover, meeting the write-heavy, short-lived requirements. Azure Front Door with Azure CDN provides global load balancing and caching for the read-heavy, rarely updated product catalog, ensuring low-latency content delivery from the nearest point of presence.
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 Cosmos DB for session state and Azure Front Door with Azure CDN for catalog.
Why this is correct
Azure Cosmos DB is the correct choice for session state because it provides multi-region writes with automatic failover, ensuring globally distributed users can write and read session data with low latency and no single point of failure. Its tunable consistency levels allow you to balance performance against data freshness, while Azure Front Door with Azure CDN delivers the global catalog by routing dynamic traffic intelligently and caching static/mixed content at the edge, offloading origin servers and improving read-heavy catalog performance.
- ✗
Azure Cache for Redis for session state and Azure Front Door for catalog.
Why it's wrong here
Azure Cache for Redis is a fast in-memory data store, but it is not designed to be the primary durable store for session state. In a global e-commerce scenario, a virtual machine or service restart, eviction policy, or cache node failure can silently erase session data, breaking user carts and authentication state; persistence features are secondary and often risk data loss for performance. Therefore, using Redis alone for session state is unreliable, even though it works well as a caching layer in front of a durable datastore.
- ✗
Azure Table Storage for session state and Azure Front Door for catalog.
Why it's wrong here
Azure Table Storage is a scalable NoSQL key-value store, but it lacks multi-region write support, meaning all writes go to a single primary region and replicas are only passively copied. During an Azure regional outage, a manual or automatic geo-failover can take minutes, and until then users in other regions cannot update their sessions seamlessly. This makes it a poor fit for a globally distributed e-commerce platform where session state must be continuously writable and available across all geo-regions at all times.
- ✗
Azure SQL Database with geo-replication for both.
Why it's wrong here
Azure SQL Database with geo-replication provides strong consistency and reliable transactional storage, but for session state it is both cost-ineffective and operationally heavy, requiring substantial compute resources to handle high-frequency, low-complexity reads and writes. Geo-replication is asynchronous, so a regional failover can cause a few seconds of data loss and service interruption, which is unacceptable for active sessions. For the catalog, SQL Database lacks the edge-caching benefits of Front Door and CDN, and it introduces unnecessary cost and latency when compared to a CDN-backed globally distributed catalog.
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Senior Network & Security Engineer · founder of Courseiva
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