AZ-900 Describe Azure architecture and services Practice Question
Which Azure compute option is best for running a batch processing job that can be interrupted and resumed without data loss, at the lowest possible cost?
⚠ Common exam trap
A common mix-up: candidates confuse Azure Spot VMs with Reserved Instances or Dedicated Hosts, mistakenly thinking that any discounted option (like Reserved Instances) is best for cost savings, but they fail to recognize that only Spot VMs are designed for interruptible workloads and provide the lowest cost for batch jobs that can tolerate eviction.
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 Spot Virtual Machines
Azure Spot Virtual Machines are designed for interruptible workloads, such as batch processing jobs, because they use unused Azure capacity at a significant discount (up to 90% compared to pay-as-you-go). When Azure needs the capacity back, these VMs can be evicted with a 30-second notice, but the job can be resumed without data loss if the application is designed to handle interruptions (e.g., using checkpointing or saving state to persistent storage). This makes Spot VMs the most cost-effective option for fault-tolerant, interruptible batch processing.
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 Reserved VM Instances
Why it's wrong here
Azure Reserved VM Instances require a one- or three-year commitment for a specific region and VM size in exchange for a discounted hourly rate. Unlike Spot VMs, they are not evictable — the capacity is reserved and the workload runs continuously for the full term. This is designed for predictable, steady-state production workloads, not for transient or interruptible batch jobs that would benefit from Spot's significantly lower, interruption-based pricing.
- ✓
Azure Spot Virtual Machines
Why this is correct
Azure Spot Virtual Machines let you consume unused Azure compute capacity at discounts up to 90%, with the critical caveat that Azure can evict them at any time with a 30-second notice when capacity is needed elsewhere. They support eviction policies like delete or deallocate and allow a max price to cap your spending per hour. This makes them ideal for stateless, interruptible jobs like batch processing and dev/test environments, but not for critical, stateful workloads that require uninterrupted availability.
- ✗
Azure Dedicated Host
Why it's wrong here
Azure Dedicated Host gives you a physical server dedicated to your organization, providing hardware-level isolation for compliance or licensing requirements. It is billed at a premium per host and offers no discount based on interruption tolerance, nor can Azure reclaim it for other tenants. Spot VMs, by contrast, run on shared surplus capacity at a steep discount, with the trade-off that they may be evicted — the opposite of Dedicated Host's guaranteed but expensive model.
- ✗
Standard Pay-as-you-Go VMs
Why it's wrong here
Standard Pay-as-you-go VMs charge the full per-hour rate with no upfront commitment or volume discount, and they are backed by a capacity guarantee that prevents eviction. While this model is flexible, it is the most expensive on-demand option when compared to Spot VMs, which can be 70–90% cheaper for workloads that can tolerate interruptions. For an interruptible batch job, choosing pay-as-you-go means paying a premium for a guarantee you do not need.
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