AZ-305 Design data storage solutions Practice Question
A company deploys a web application on Azure VMs. The application stores session state and frequently accessed product data. They need a low-latency, in-memory cache to reduce database load and improve response times. The cache must be managed and support data persistence with replication across availability zones within the region. Which Azure service and tier should they choose?
⚠ Common exam trap
Many candidates confuse the Standard tier's replication (which is within a single datacenter) with zone redundancy, or assume Enterprise tier is always better for persistence, when Premium tier specifically offers both persistence and zone redundancy at a lower cost.
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 (Premium tier)
Azure Cache for Redis Premium tier is the correct choice because it supports data persistence (RDB/AOF), replication across availability zones via zone redundancy, and provides low-latency, in-memory caching for session state and product data. The Basic tier lacks replication and persistence, Standard tier offers replication but not zone redundancy or persistence, and Enterprise tier is overkill for this scenario, adding unnecessary cost and complexity.
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 Cache for Redis (Premium tier)
Why this is correct
Azure Cache for Redis Premium tier is the appropriate choice because it uniquely combines zone-redundant replication—spreading the primary and replica nodes across Azure availability zones—with built-in data persistence options (RDB snapshots and AOF append-only file). This gives you both high availability and durability of cached data, enabling you to survive an entire zone failure without losing data. Being fully managed, it also supports Redis clustering for scaling out beyond the memory limit of a single node, which is why it meets the production requirements.
- ✗
Azure Cache for Redis (Basic tier)
Why it's wrong here
The Basic tier is a single-node cache that offers no service-level agreement, no replication, and no data persistence. If that single node restarts or the underlying VM is patched, all cached data is lost and the application experiences downtime. It is intended only for development and testing scenarios, not for any production workload that requires high availability or durable storage.
- ✗
Azure Cache for Redis (Standard tier)
Why it's wrong here
The Standard tier runs two replicas in the same Azure region, yielding a 99.9% SLA and protecting against individual node failures, but it does not support data persistence (RDB/AOF) or zone-redundant deployment. Because the replicas are typically pinned within the same datacenter/availability zone, a zone-wide outage can take the entire cache offline and any non-resilient data is lost. This tier addresses HA but fails the persistence and cross-zone durability requirements.
- ✗
Azure Cache for Redis (Enterprise tier)
Why it's wrong here
The Enterprise tier supports data persistence and zone redundancy, but it is based on Redis Enterprise, which is more expensive. While it meets requirements, the Premium tier is the appropriate and more common choice for in-region zone redundancy and persistence.
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