AZ-900 Describe Azure architecture and services Practice Question
A company deploys a web application on Azure App Service. During a marketing campaign, they expect traffic to double. The app uses a Standard tier App Service plan. They want to ensure that the additional load is handled without performance degradation while keeping costs minimal. Which action should they take?
⚠ Common exam trap
The trap is that candidates may choose to enable autoscale (C) thinking it's the most automated and cost-effective solution, but for a predictable doubling of traffic during a campaign, manual scale-out (A) is simpler and avoids potential scaling delays. Autoscale is available on Standard tier, but it requires configuring rules and may not be necessary for a known traffic increase. Also, scaling up (B) to Premium is unnecessary and more expensive.
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
✓
Scale out the App Service plan by increasing the instance count.
Scaling out (increasing instance count) for the Standard tier App Service plan allows the application to handle the doubled traffic by distributing requests across multiple instances, ensuring no performance degradation. This approach is cost-minimal because the Standard tier supports manual scale-out without requiring a tier upgrade, and you only pay for the additional instances while they are needed.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Scale out the App Service plan by increasing the instance count.
Why this is correct
Scaling out increases the number of VM instances running the App Service plan, allowing Azure's built-in load balancer to distribute incoming requests across all instances. For a predictable doubling of traffic, adding instances provides immediate additional compute capacity and is more cost-effective than scaling up, because you pay per-second for these standard-tier instances and can later scale back in. This manual operation takes effect within seconds to minutes, directly addressing the expected spike now.
- ✗
Scale up the App Service plan to a Premium tier for more resources.
Why it's wrong here
Scaling up moves the App Service plan to a higher tier (e.g., Premium) which increases per-instance vCPU, memory, and storage, but it does not increase the number of instances; a single larger VM still has a fixed connection and request-handling ceiling. For an anticipated doubling of concurrent users, scaling up is usually more expensive because you pay premium-tier pricing on every instance for the entire duration, and it provides less elasticity than scaling out. The temporary load would be better handled by adding more standard instances, which offers cheaper marginal capacity and permits easier scale-back.
When this WOULD be correct
A question where the application requires more CPU, memory, or I/O per instance than the current tier can provide, and cost is less of a concern. For example: 'A company's web app on Basic tier is experiencing high CPU usage even with multiple instances. They need to improve performance without adding more instances.'
- ✗
Enable autoscale on the existing plan to let Azure handle scaling automatically.
Why it's wrong here
Enabling autoscale is a proactive configuration that sets rules for minimum/maximum instance counts based on metrics like CPU or request count, but it does not create additional instances immediately unless the metric thresholds are currently breached. For an expected doubling of traffic, relying on autoscale to trigger at the exact moment traffic increases risks a lag while instances spin up, potentially causing latency or throttling during the surge. Autoscale is best configured ahead of time as a long-term solution, but the question asks for an immediate action, so scaling out manually now is the direct response.
When this WOULD be correct
A company expects variable traffic patterns (e.g., seasonal spikes) and wants to automatically adjust resources to handle load without manual intervention, while staying within the existing plan's instance limits.
- ✗
Deploy Azure CDN to cache static content.
Why it's wrong here
Deploying Azure CDN caches static content at edge locations closer to users, reducing latency and offloading some request volume from the App Service origin, but it does not increase the compute capacity of the App Service plan itself. Dynamic requests, authentication, API calls, and any uncached content still hit the original instances, so the web app's ability to handle concurrent users remains constrained by the existing instance count. CDN is a performance optimization for content delivery, not a scaling mechanism for compute resources, and it would not prevent the App Service from exhausting its connections or CPU during a traffic spike.
When this WOULD be correct
A company deploys a global web application with high traffic from multiple regions. They want to improve load times and reduce server load for static assets (e.g., images, CSS). In this scenario, deploying Azure CDN would be correct to cache content at edge locations.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The AZ-900 exam frequently reuses these exact scenarios with slightly different constraints.
✓Scale out the App Service plan by increasing the instance count.Correct answer▾
Why this is correct
Scaling out increases the number of VM instances running the App Service plan, allowing Azure's built-in load balancer to distribute incoming requests across all instances. For a predictable doubling of traffic, adding instances provides immediate additional compute capacity and is more cost-effective than scaling up, because you pay per-second for these standard-tier instances and can later scale back in. This manual operation takes effect within seconds to minutes, directly addressing the expected spike now.
✗Scale up the App Service plan to a Premium tier for more resources.Wrong answer — click to see why▾
Why this is wrong here
Scaling up to Premium tier increases per-instance resources but costs more, while the question emphasizes minimal cost. The Standard tier can handle the load by scaling out (adding instances), which is cheaper than upgrading the entire plan.
★ When this WOULD be the correct answer
A question where the application requires more CPU, memory, or I/O per instance than the current tier can provide, and cost is less of a concern. For example: 'A company's web app on Basic tier is experiencing high CPU usage even with multiple instances. They need to improve performance without adding more instances.'
Why candidates choose this
Candidates may think that more powerful instances (scale up) are always better for handling increased load, and they might overlook that scaling out (adding instances) is often more cost-effective for stateless web apps.
✗Enable autoscale on the existing plan to let Azure handle scaling automatically.Wrong answer — click to see why▾
Why this is wrong here
Autoscale adjusts instance count based on metrics, but the Standard tier has a fixed maximum instance count (typically 3-10 depending on plan). Doubling traffic may exceed this limit, causing performance degradation. Manual scaling out ensures sufficient capacity.
★ When this WOULD be the correct answer
A company expects variable traffic patterns (e.g., seasonal spikes) and wants to automatically adjust resources to handle load without manual intervention, while staying within the existing plan's instance limits.
Why candidates choose this
Candidates assume autoscale is a cost-effective, hands-off solution for any traffic increase, not realizing that the Standard tier's instance limit may be insufficient for a predictable doubling of traffic.
✗Deploy Azure CDN to cache static content.Wrong answer — click to see why▾
Why this is wrong here
Azure CDN caches static content to reduce latency and offload traffic from the origin, but it does not increase the compute capacity of the App Service plan. The primary concern is handling doubled traffic without performance degradation, which requires more compute resources, not just caching.
★ When this WOULD be the correct answer
A company deploys a global web application with high traffic from multiple regions. They want to improve load times and reduce server load for static assets (e.g., images, CSS). In this scenario, deploying Azure CDN would be correct to cache content at edge locations.
Why candidates choose this
Candidates may think CDN can handle increased traffic by offloading requests, but they overlook that the question focuses on compute capacity for dynamic processing, not static content delivery.
Analysis generated from the official AZ-900blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This AZ-900 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-900 exam.