MS-900 Describe cloud concepts Practice Question
A company uses a cloud service where they pay only for the compute hours their virtual machines run. They can increase or decrease the number of VMs instantly based on demand. Which two cloud computing characteristics are demonstrated? (Choose two.)
⚠ Common exam trap
A common mix-up: candidates confuse 'on-demand self-service' with the ability to instantly scale resources, but on-demand self-service specifically refers to the user's ability to provision resources without provider intervention, not the elasticity of scaling.
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
✓
Rapid elasticity
B is correct because rapid elasticity allows the company to instantly increase or decrease the number of virtual machines based on demand, scaling resources up or down automatically. C is correct because measured service ensures that the company pays only for the compute hours their VMs run, with usage metered and billed accordingly.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
On-demand self-service
Why it's wrong here
On-demand self-service is a cloud characteristic where a consumer can unilaterally provision computing resources, such as virtual machines or storage, automatically without requiring human interaction with the service provider. While the company may be using this capability to scale VMs, the specific detail about paying only for hours used and scaling based on demand highlights billing and elasticity rather than the provisioning mechanism itself. The central focus of self-service is the 'no human interaction' aspect, not the metered billing or dynamic scaling described in the scenario.
- ✓
Rapid elasticity
Why this is correct
Rapid elasticity is the cloud characteristic that enables resources to be provisioned and released elastically, often automatically, to scale outward and inward commensurate with demand. In this scenario, the company's ability to increase or decrease the number of virtual machines based on demand is a textbook example of rapid elasticity, as it directly addresses the agility and scalability of resource allocation. This elasticity is what allows the company to align its resource usage with actual workload, rather than over-provisioning for peak demand.
- ✓
Measured service
Why this is correct
Measured service refers to the cloud capability where resource usage is metered, monitored, and reported to provide transparency and control for both the provider and the consumer. Paying only for the compute hours used is a direct manifestation of measured service, because billing is based on the measured consumption of resources, such as virtual machine compute time. This usage-based billing model differentiates cloud computing from traditional on-premises IT, where costs are incurred upfront regardless of actual utilization.
- ✗
Resource pooling
Why it's wrong here
Resource pooling describes the provider's multi-tenant model, where computing resources are pooled to serve multiple customers, with physical and virtual resources dynamically assigned and reassigned according to demand. This characteristic gives rise to location independence, as customers typically do not control the exact resource location. However, the scenario's details about paying per hour and scaling VMs on demand do not illustrate resource pooling; they instead demonstrate metering and elasticity, which are customer-visible consumption traits rather than the provider's internal sharing architecture.
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