AZ-305 Design infrastructure solutions Practice Question
Your company is deploying a web application that experiences unpredictable traffic spikes. You need to ensure the application can handle sudden increases in load automatically without manual intervention and minimize costs during low traffic periods. Which Azure service should you use?
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
✓
Virtual Machine Scale Set with autoscale
Virtual Machine Scale Sets with autoscale rules can automatically adjust the number of VM instances based on demand. Option A (Azure App Service with manual scaling) does not autoscale automatically. Option B (Azure Functions) is for event-driven workloads, not web apps. Option D (Azure Container Instances) does not autoscale natively.
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 App Service with manual scale-out
Why it's wrong here
Azure App Service supports manual scale-out by raising the instance count through the portal, but this is a reactive process requiring an operator to detect a spike and adjust capacity. Because it cannot respond automatically to changing traffic, it risks either over-provisioning (wasteful cost) or under-provisioning (degraded performance). For a workload that needs reliable elasticity, manual scale-out fails to meet the automatic recovery requirement.
- ✗
Azure Functions with consumption plan
Why it's wrong here
Azure Functions uses a consumption plan that provides event-driven autoscaling, but it is designed for short-running, stateless, event-triggered workloads such as APIs, queue processing, or timer jobs. It is not meant to host a full web application because functions have execution time limits, can suffer cold starts, and lack a persistent server environment for long-running requests. Therefore, while it scales automatically, it is architecturally unsuitable for this scenario.
- ✓
Virtual Machine Scale Set with autoscale
Why this is correct
Virtual Machine Scale Sets with autoscale rules are the correct choice because they automatically adjust the number of VM instances based on metrics like CPU percentage, memory, or custom thresholds. This enables horizontal scaling to handle traffic spikes by adding instances and also scaling in during low demand to reduce costs. The approach is ideal for hosting web applications that require full control over the VM image, dependencies, or infrastructure-level configuration.
- ✗
Azure Container Instances
Why it's wrong here
Azure Container Instances provides fast, serverless container execution but lacks a built-in autoscale mechanism that adjusts instance counts based on load metrics. To scale containers automatically, you must add an orchestrator like Azure Kubernetes Service or deploy a separate service to manage container groups, which adds complexity and latency. For this reason, it cannot autonomously handle traffic spikes for a web application without additional external orchestration.
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.