AZ-305 Design infrastructure solutions Practice Question
Your organization is building a serverless application that processes events from Azure Event Hubs and stores results in Azure Cosmos DB. The processing logic must be scalable and cost-effective, with no idle costs. Which compute service should you use?
⚠ Common exam trap
Many candidates confuse Azure Functions with Azure Logic Apps, assuming both are serverless, but Logic Apps is designed for workflow integration and not for high-throughput, event-stream processing, leading to incorrect cost and performance assumptions.
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 Functions
Azure Functions is the correct choice because it provides a serverless, event-driven compute service that can be triggered directly by Azure Event Hubs. It scales automatically based on the number of events, and you only pay for execution time, resulting in zero idle costs. This makes it ideal for processing streaming events in a cost-effective, scalable manner without managing infrastructure.
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 Functions
Why this is correct
Azure Functions is a true serverless compute service designed for event-driven architectures. It runs on the consumption plan where you pay only for execution time while the platform automatically scales out in response to incoming events and scales to zero when idle, eliminating idle cost. Tight integration with Azure triggers (e.g., HTTP, Event Grid, Service Bus, Blob) makes it the optimal choice for high-throughput, short-lived processing tasks where granular scaling and cost efficiency are required.
- ✗
Azure Container Instances
Why it's wrong here
Azure Container Instances (ACI) provides per-second billing for running containers, which means you pay for the container the entire time it is alive, even when it is not processing any events. While ACI is a fast way to run containers without managing virtual machines, it does not offer built-in event-driven scaling based on message volume and requires explicit start/stop or external orchestration to achieve scale-to-zero behavior. This reserved-resource model conflicts with the serverless pay-for-execution requirement and introduces idle costs that are unacceptable for an event-driven application.
- ✗
Azure Logic Apps
Why it's wrong here
Azure Logic Apps is a cloud workflow service for automating business processes and integrating applications using 200+ connectors and a visual designer. However, each action consumes execution time and carries a per-action pricing model, making it substantially more expensive and slower when processing high-frequency events or large message streams. Logic Apps also lacks the native, sub-second autoscaling behavior of Azure Functions, being designed instead for moderate-rate workflow orchestration rather than raw event processing.
- ✗
Azure Kubernetes Service
Why it's wrong here
Azure Kubernetes Service (AKS) is a managed Kubernetes platform that requires you to provision and pay for node VM instances in your cluster, regardless of how much your application is actually used. The cluster incurs continuous infrastructure cost, and you must manage node pools, autoscaler, and container scheduling, which adds operational overhead. Even though serverless-like features such as virtual nodes or Knative can be added, the base AKS offering does not provide event-driven scale-to-zero compute and is therefore not a serverless or pay-per-execution solution.
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This AZ-305 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-305 exam.