Cost Blind Spot — Azure Fundamentals (AZ-900)
The architecturally correct answer was also the most expensive. The exam wanted the cost-optimized option that still meets requirements.
Maximum Resilience Isn't Always the Right Answer
The exam phrases these questions around 'most cost-effective' or 'meets requirements at lowest cost' — language candidates often skim. The distractor maximizes redundancy or geo-replication in ways the scenario never requested. When 'meets requirements' appears alongside a cost modifier, the correct answer satisfies the functional floor, not the architectural ceiling. Selecting the most capable option when the scenario sets a cost constraint is a scoring mistake, not a safe choice.
The Scenario
A company needs to generate thumbnails from user-uploaded images. You design a solution with Azure Kubernetes Service and GPU-enabled nodes for fast processing. The correct answer uses Azure Functions with a Consumption plan triggered by Blob Storage events — images are under 10MB, processing takes 2-3 seconds per image, and the scenario said "cost-optimize for variable upload volume." AKS with GPU nodes costs $1,000+/month in base compute even at idle. Functions at 100,000 executions/month costs under $2. The exam tests whether you recognize that "image processing" does not automatically mean "GPU compute."
How to Spot It
- •Azure Spot VMs give up to 90% savings over pay-as-you-go for fault-tolerant workloads. Batch rendering, data analysis, and dev/test environments are the canonical Spot workloads. If the scenario describes interruptible work, Spot VMs or Spot-enabled AKS node pools are the cost-optimized answer.
- •Azure Cosmos DB charges for provisioned RU/s even when idle. A database provisioned at 10,000 RU/s costs ~$580/month. If the scenario describes "occasional reads" or "variable traffic," serverless Cosmos DB (pay per RU consumed) or Azure SQL Serverless eliminates idle costs.
- •Azure Front Door Premium costs ~$330/month base. Azure CDN Standard costs ~$0.08/GB. For a static website serving 100GB/month, CDN costs $8 vs. Front Door at $330+. The exam tests whether you select the CDN tier that matches the traffic profile, not the one with the most features.
Decision Rules
Choose the tool that compares existing on-premises CapEx against projected Azure OpEx (TCO Calculator) versus a tool that estimates only Azure-side resource costs (Pricing Calculator), given that the stated requirement is a before-and-after savings justification.
Domain Coverage
Difficulty Breakdown
Related Patterns