Azure Container Instances: Ideal for Intermittent Container Workloads with Per-Second Billing
A company has a simple containerized web application that runs in a single container. The application processes a workload for a few minutes every hour and remains idle the rest of the time. The company wants to deploy the container in Azure without managing any virtual machines or container orchestrators. They also want to pay only for the time the container is actually running, with no cost when idle. Which Azure compute service should the company use?
Quick Answer
Azure Container Instances is the correct choice because it enables you to run a containerized application without managing any virtual machines or container orchestrators, and its per-second billing model means you pay only for the time the container is actively running, with no cost when idle. This perfectly matches the requirement for a simple, single-container workload that processes data for a few minutes each hour. On the Microsoft Azure Fundamentals AZ-900 exam, this scenario tests your understanding of serverless compute options and their cost models, often contrasting ACI with services like Azure Kubernetes Service or Azure App Service. A common trap is selecting a service that requires ongoing management or charges for allocated resources even when idle. Remember the memory tip: “ACI = Always Charged for Intervals” — meaning you only pay for the exact seconds your container is in use, making it ideal for intermittent container workloads.
⚠ Common exam trap
Test-takers frequently confuse Azure App Service's container support with a serverless container service, not realizing that App Service still requires a continuously running plan (e.g., Basic, Standard) that incurs charges even when the container is idle.
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 Container Instances
Azure Container Instances (ACI) is the correct choice because it allows you to run a containerized application without managing any underlying virtual machines or container orchestrators like Kubernetes. ACI supports a per-second billing model, meaning you only pay for the compute resources consumed while the container is actively running, and incur no cost when the container is stopped or idle. This aligns perfectly with the company's requirement of a simple, single-container workload that runs intermittently.
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
Why it's wrong here
Azure App Service can deploy containers, but it runs continuously and bills per hour (or per plan), not per second of actual runtime. It also requires a plan that is always running, which does not match the requirement to pay only for active processing minutes.
When this WOULD be correct
A company needs to host a web application with a custom domain and SSL, requiring built-in scaling and load balancing, without managing infrastructure. Azure App Service would be correct.
- ✓
Azure Container Instances
Why this is correct
Azure Container Instances (ACI) is the correct choice. It allows you to run containers directly on Azure without managing VMs or orchestrators. ACI bills per second of container execution and has no active cost when the container is stopped, matching the pay-per-use requirement perfectly.
- ✗
Azure Virtual Machine Scale Sets
Why it's wrong here
Azure Virtual Machine Scale Sets require you to manage virtual machines (even though they can be patched and scaled automatically). You pay for the underlying VMs regardless of whether the container is actively processing, and you must manage the container runtime environment. This does not meet the no-VM-management or pay-per-second requirements.
When this WOULD be correct
A company needs to run a containerized application that requires high availability, auto-scaling across multiple VMs, and can tolerate managing VMs, with consistent traffic that justifies running VMs continuously.
- ✗
Azure Kubernetes Service
Why it's wrong here
Azure Kubernetes Service (AKS) is a managed Kubernetes orchestrator, but it still requires you to manage worker node VMs (even if Microsoft manages the control plane). You pay for the node VMs continuously, and there is additional operational overhead for the Kubernetes configuration. It is not serverless and does not offer per-second billing for container execution.
When this WOULD be correct
A company needs to deploy a multi-container application with complex scaling, service discovery, and rolling updates, and is willing to manage the orchestrator's control plane (or use a managed version) to gain advanced orchestration features. They also need to run containers continuously, not just on-demand.
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.
✓Azure Container InstancesCorrect answer▾
Why this is correct
Azure Container Instances (ACI) is the correct choice. It allows you to run containers directly on Azure without managing VMs or orchestrators. ACI bills per second of container execution and has no active cost when the container is stopped, matching the pay-per-use requirement perfectly.
✗Azure App ServiceWrong answer — click to see why▾
Why this is wrong here
Azure App Service requires the application to be always running and charges for the underlying plan even when idle, so it does not meet the requirement of paying only for actual running time.
★ When this WOULD be the correct answer
A company needs to host a web application with a custom domain and SSL, requiring built-in scaling and load balancing, without managing infrastructure. Azure App Service would be correct.
Why candidates choose this
Candidates may confuse App Service's support for containers with the pay-per-use model of Container Instances, overlooking that App Service charges for the plan continuously.
✗Azure Virtual Machine Scale SetsWrong answer — click to see why▾
Why this is wrong here
Azure Virtual Machine Scale Sets require managing VMs and do not provide a serverless container experience; they also incur costs for idle VMs, unlike the pay-per-execution model needed.
★ When this WOULD be the correct answer
A company needs to run a containerized application that requires high availability, auto-scaling across multiple VMs, and can tolerate managing VMs, with consistent traffic that justifies running VMs continuously.
Why candidates choose this
Candidates may think scale sets can handle containerized workloads and auto-scaling, but overlook the requirement to avoid managing VMs and the need for zero cost when idle.
✗Azure Kubernetes ServiceWrong answer — click to see why▾
Why this is wrong here
Azure Kubernetes Service (AKS) is a managed container orchestrator, but the question explicitly states the company does not want to manage any container orchestrators. AKS still requires managing the orchestrator plane, and it incurs costs even when the container is idle.
★ When this WOULD be the correct answer
A company needs to deploy a multi-container application with complex scaling, service discovery, and rolling updates, and is willing to manage the orchestrator's control plane (or use a managed version) to gain advanced orchestration features. They also need to run containers continuously, not just on-demand.
Why candidates choose this
Candidates may think AKS is the only Azure container service and overlook the 'no orchestrator management' requirement, or they may confuse AKS's managed control plane with a fully serverless offering.
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?”
Go deeper
Related to this question
Learn chapter
Azure Regions and Geographies
Key term
Workload
A workload is any discrete application, service, or function that runs on a computing resource, consuming CPU, memory, storage, or network capacity.
Key term
Container
A container is a lightweight, standalone software package that includes everything needed to run an application, such as code, runtime, system tools, and libraries.
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Same concept, more angles
3 more ways this is tested on AZ-900
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company wants to run a containerized application that responds to HTTP requests. They want to deploy it without managing any virtual machines or orchestration. Which Azure service is the simplest option?
medium- A.Azure Kubernetes Service
- ✓ B.Azure Container Instances
- C.Azure Virtual Machines
- D.Azure App Service
Why B: Azure Container Instances (ACI) is the simplest option because it allows you to run a containerized application directly in Azure without managing any underlying virtual machines or orchestration. ACI automatically starts the container, assigns a public IP address, and handles HTTP requests on port 80/443, making it ideal for event-driven or stateless workloads that need rapid deployment.
Variation 2. A company needs to run a containerized application without managing any virtual machines or cluster orchestration. Which Azure service is best suited for this?
medium- ✓ A.Azure Container Instances
- B.Azure Kubernetes Service
- C.Azure App Service
- D.Azure Batch
Why A: Azure Container Instances (ACI) is the correct choice because it allows you to run a containerized application directly on Azure without provisioning or managing any underlying virtual machines, cluster orchestration, or scheduling. ACI provides a serverless, per-second billing model, making it ideal for simple, isolated containers that do not require the complexity of a full orchestration platform.
Variation 3. A company wants to run a containerized application quickly without managing any virtual machines or orchestration infrastructure. They just need to start a container and have it run. Which Azure service is best suited for this?
medium- ✓ A.Azure Container Instances
- B.Azure Kubernetes Service
- C.Azure App Service
- D.Azure Functions
Why A: Azure Container Instances (ACI) is the correct choice because it provides a serverless container platform that allows you to run a container directly without managing any underlying virtual machines or orchestration infrastructure. You simply specify the container image and resource requirements, and ACI launches the container in seconds, making it ideal for quick, isolated container workloads.
JA
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.