VM pricing models in Azure - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Azure VM Pricing Models

Which Azure VM pricing model offers the lowest cost for workloads that can be interrupted and restarted?

A Pay-as-you-go pricing

B Spot Instances

C Reserved Instances

D Dedicated Hosts

💡 Hint

Think about pricing models that allow Azure to reclaim capacity when needed.

Spot Instances offer the lowest cost but can be evicted when Azure needs capacity, making them suitable for interruptible workloads.

❓ Architecture

intermediate

Choosing VM Pricing for Long-Term Stable Workloads

You have a stable, long-running application that will run continuously for 3 years. Which Azure VM pricing model should you choose to minimize cost?

A Spot Instances

B Pay-as-you-go pricing

C Reserved Instances with 3-year term

D Dedicated Hosts

💡 Hint

Consider pricing models that offer discounts for long-term commitments.

Reserved Instances with a 3-year term provide significant discounts for long-term, stable workloads by committing to usage upfront.

❓ service_behavior

advanced

Behavior of Spot Instances During Capacity Reclamation

What happens to an Azure Spot VM when Azure needs the capacity back?

A The VM receives a notification and is evicted after a short period.

B The VM is deallocated immediately without warning.

C The VM is paused and resumed later automatically.

D The VM continues running until manually stopped.

💡 Hint

Think about how Azure informs users before reclaiming Spot VM capacity.

Azure Spot VMs receive a notification before eviction, allowing a short time to save state or shut down gracefully.

❓ security

advanced

Security Considerations for Dedicated Hosts

Which security advantage does using Azure Dedicated Hosts provide compared to shared VM pricing models?

A Automatic encryption of all VM data at rest

B No need for network security groups

C Built-in DDoS protection for all VMs

D Physical isolation of VMs on dedicated hardware for compliance needs

💡 Hint

Consider physical hardware isolation for compliance and security.

Dedicated Hosts provide physical isolation by dedicating hardware to a single customer, helping meet compliance and security requirements.

✅ Best Practice

expert

Optimizing Cost with Mixed VM Pricing Models

You need to run a batch processing job that can tolerate interruptions but also requires some guaranteed capacity. Which combination of Azure VM pricing models is best to optimize cost and reliability?

A Use a mix of Spot Instances for interruptible tasks and Reserved Instances for guaranteed capacity

B Use Spot Instances for all batch jobs to minimize cost

C Use Dedicated Hosts for all batch jobs to ensure isolation

D Use only Pay-as-you-go VMs for all batch jobs

💡 Hint

Think about balancing cost savings with reliability needs.

Combining Spot Instances for interruptible tasks with Reserved Instances for guaranteed capacity balances cost savings and reliability.

Practice

1. Which Azure VM pricing model allows you to pay only for the time you use without any long-term commitment?

easy

A. Spot VMs

B. Reserved Instances

C. Hybrid Benefit

D. Pay-as-you-go

Solution

1. Step 1: Understand Pay-as-you-go model

   This model charges you based on actual usage with no upfront commitment.

2. Step 2: Compare with other models

   Reserved Instances require upfront commitment, Spot VMs can be interrupted, Hybrid Benefit is a discount on licenses.

3. Final Answer:

   Pay-as-you-go -> Option D

4. Quick Check:

   Flexible payment without commitment = Pay-as-you-go [OK]

Hint: Pay only for what you use with no upfront cost [OK]

Common Mistakes:

• Confusing Reserved Instances with Pay-as-you-go
• Thinking Spot VMs are always available
• Mixing Hybrid Benefit with pricing models

2. Which of the following is the correct description of Spot VMs in Azure?

easy

A. VMs that offer the lowest price but can be evicted anytime

B. VMs with a fixed monthly cost and no interruptions

C. VMs reserved for one year with upfront payment

D. VMs that use existing licenses for cost savings

Solution

1. Step 1: Identify Spot VMs characteristics

   Spot VMs provide the lowest price but can be interrupted or evicted when Azure needs capacity.

2. Step 2: Eliminate other options

   Fixed monthly cost applies to Reserved Instances, upfront payment is for Reserved Instances, license reuse is Hybrid Benefit.

3. Final Answer:

   VMs that offer the lowest price but can be evicted anytime -> Option A

4. Quick Check:

   Lowest cost but interruptible = Spot VMs [OK]

Hint: Spot VMs are cheap but can be stopped anytime [OK]

Common Mistakes:

• Assuming Spot VMs have fixed pricing
• Confusing Spot VMs with Reserved Instances
• Thinking Hybrid Benefit applies to Spot VMs

3. Consider you have a workload that runs continuously for 3 years. Which pricing model will most likely save you the most money?

medium

A. Pay-as-you-go

B. Reserved Instances

C. Hybrid Benefit

D. Spot VMs

Solution

1. Step 1: Analyze workload duration

   A continuous 3-year workload benefits from long-term commitment discounts.

2. Step 2: Match pricing model to workload

   Reserved Instances offer significant savings for long-term use compared to Pay-as-you-go or Spot VMs.

3. Final Answer:

   Reserved Instances -> Option B

4. Quick Check:

   Long-term continuous use = Reserved Instances [OK]

Hint: Long-term use? Choose Reserved Instances [OK]

Common Mistakes:

• Choosing Pay-as-you-go for long-term workloads
• Selecting Spot VMs for continuous workloads
• Confusing Hybrid Benefit with pricing model alone

4. You tried to deploy a Spot VM but it was evicted unexpectedly. What is the most likely reason?

medium

A. Azure needed the capacity and reclaimed the Spot VM

B. You exceeded your reserved instance quota

C. You did not apply Hybrid Benefit correctly

D. Your Pay-as-you-go subscription expired

Solution

1. Step 1: Understand Spot VM eviction

   Spot VMs can be evicted anytime Azure needs capacity for other workloads.

2. Step 2: Rule out other causes

   Reserved instance quota does not affect Spot VMs, Hybrid Benefit is unrelated to eviction, subscription expiration stops all VMs.

3. Final Answer:

   Azure needed the capacity and reclaimed the Spot VM -> Option A

4. Quick Check:

   Spot VM eviction = Azure capacity needs [OK]

Hint: Spot VMs can be stopped anytime Azure needs space [OK]

Common Mistakes:

• Blaming reserved instance quota for Spot eviction
• Thinking Hybrid Benefit prevents eviction
• Assuming subscription expiration causes eviction only

5. You want to run a batch job that can tolerate interruptions and save the most money. Which Azure VM pricing model should you choose and why?

hard

A. Reserved Instances because they offer the lowest price for long-term use

B. Pay-as-you-go because it offers flexibility without upfront cost

C. Spot VMs because they offer the lowest price but can be interrupted

D. Hybrid Benefit because it uses existing licenses to reduce cost

Solution

1. Step 1: Identify workload tolerance

   The batch job can handle interruptions, so a pricing model with possible evictions is acceptable.

2. Step 2: Match pricing model to workload needs

   Spot VMs offer the lowest price but can be interrupted, fitting the batch job's tolerance and cost-saving goal.

3. Step 3: Eliminate other options

   Reserved Instances are for long-term steady use, Pay-as-you-go is flexible but more expensive, Hybrid Benefit reduces license cost but not VM price.

4. Final Answer:

   Spot VMs because they offer the lowest price but can be interrupted -> Option C

5. Quick Check:

   Interruptible and cheap = Spot VMs [OK]

Hint: Interruptible jobs? Choose Spot VMs for best savings [OK]

Common Mistakes:

• Choosing Reserved Instances for interruptible jobs
• Confusing Hybrid Benefit with pricing model
• Ignoring interruption tolerance in choice