Spot VMs for cost savings in Azure - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Spot VM eviction behavior

You deploy an Azure Spot VM to save costs. What happens when Azure needs the capacity back?

A The Spot VM is immediately deallocated without warning.

B The Spot VM continues running until you manually stop it.

C The Spot VM automatically converts to a standard VM without interruption.

D The Spot VM receives a notification and is evicted after a short time.

💡 Hint

Think about how Azure informs you before stopping a Spot VM.

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

❓ Architecture

intermediate

Designing a resilient app with Spot VMs

You want to use Spot VMs for batch processing but avoid job failures when VMs are evicted. Which architecture best supports this?

A Combine Spot VMs with standard VMs in a scale set and use a queue to track jobs.

B Deploy Spot VMs without any monitoring or retry logic.

C Use only standard VMs to avoid eviction interruptions.

D Use Spot VMs with no backup and restart jobs manually if evicted.

💡 Hint

Think about how to handle interruptions automatically.

Combining Spot and standard VMs with a queue allows jobs to be retried if Spot VMs are evicted, improving resilience.

❓ Configuration

advanced

Configuring eviction policy for Spot VMs

Which eviction policy setting allows a Spot VM to be stopped and deallocated instead of deleted upon eviction?

A Set eviction policy to 'Deallocate'.

B Set eviction policy to 'Stop'.

C Set eviction policy to 'Delete'.

D Set eviction policy to 'Retain'.

💡 Hint

Consider how to keep the VM's disk after eviction.

The 'Deallocate' eviction policy stops the VM and keeps the disk, allowing restart later.

❓ security

advanced

Security considerations for Spot VMs

What is a key security best practice when using Spot VMs in Azure?

A Disable all network security groups to improve performance.

B Allow unrestricted inbound traffic to Spot VMs for easy access.

C Use managed identities and restrict access with network security groups.

D Store all secrets directly on the Spot VM's local disk.

💡 Hint

Think about secure access and identity management.

Using managed identities and network security groups helps secure Spot VMs despite their transient nature.

❓ service_behavior

expert

Spot VM pricing and availability behavior

Which statement correctly describes how Azure Spot VM pricing and availability behave?

A Spot VM prices are fixed and availability is guaranteed 24/7.

B Spot VM prices vary based on supply and demand, and availability can be interrupted anytime.

C Spot VMs automatically switch to standard VMs when prices rise.

D Spot VMs have a monthly quota limiting usage, but prices never change.

💡 Hint

Consider how cloud providers manage excess capacity.

Spot VM prices fluctuate with supply and demand, and VMs can be evicted when capacity is needed.

Practice

1. What is the main benefit of using Azure Spot VMs?

easy

A. They automatically scale without any configuration.

B. They guarantee 100% uptime for critical applications.

C. They provide cheaper compute by using spare capacity.

D. They offer unlimited storage space for virtual machines.

Solution

1. Step 1: Understand Spot VM purpose

   Spot VMs use unused cloud capacity to offer lower prices.

2. Step 2: Compare benefits

   Unlike regular VMs, Spot VMs are cheaper but can be evicted when capacity is needed.

3. Final Answer:

   They provide cheaper compute by using spare capacity. -> Option C

4. Quick Check:

   Spot VMs = cheaper compute [OK]

Hint: Spot VMs save cost by using spare capacity [OK]

Common Mistakes:

• Thinking Spot VMs guarantee uptime
• Confusing Spot VMs with auto-scaling
• Assuming Spot VMs provide extra storage

2. Which of the following is the correct way to set a Spot VM priority in Azure CLI?

easy

A. az vm create --priority High

B. az vm create --priority Spot

C. az vm create --spot-priority true

D. az vm create --enable-spot

Solution

1. Step 1: Recall Azure CLI syntax for Spot VMs

   The correct parameter to set Spot VM priority is --priority Spot.

2. Step 2: Evaluate options

   The other options use incorrect or non-existent flags.

3. Final Answer:

   az vm create --priority Spot -> Option B

4. Quick Check:

   Spot VM priority flag = --priority Spot [OK]

Hint: Use --priority Spot to create Spot VMs [OK]

Common Mistakes:

• Using incorrect flags like --spot-priority
• Setting priority to High instead of Spot
• Assuming --enable-spot is valid

3. Consider this Azure CLI command to create a Spot VM:

az vm create --name mySpotVM --image UbuntuLTS --priority Spot --max-price 0.05

What happens if the current Spot price exceeds 0.05 USD/hour?

medium

A. The VM is converted to a regular VM automatically.

B. The VM continues running at the higher price.

C. The VM price is capped at 0.05 USD/hour but runs normally.

D. The VM is evicted (stopped) automatically.

Solution

1. Step 1: Understand max-price setting

   The max-price limits the Spot VM cost; if price rises above it, eviction occurs.

2. Step 2: Analyze behavior when price exceeds max-price

   Spot VMs are stopped or deallocated automatically when price exceeds max-price.

3. Final Answer:

   The VM is evicted (stopped) automatically. -> Option D

4. Quick Check:

   Price > max-price = VM eviction [OK]

Hint: Spot VM stops if price goes above max-price [OK]

Common Mistakes:

• Thinking VM keeps running at higher price
• Assuming price is capped automatically
• Believing VM converts to regular VM

4. You tried to create a Spot VM with this command:

az vm create --name testVM --image UbuntuLTS --priority Spot --max-price -2

What is the issue with this command?

medium

A. max-price cannot be negative; it causes an error.

B. Priority Spot is invalid syntax.

C. Image UbuntuLTS is not supported for Spot VMs.

D. VM name testVM is reserved and cannot be used.

Solution

1. Step 1: Check max-price parameter rules

   max-price must be greater than or equal to -1; other negative values are invalid.

2. Step 2: Identify error cause

   Using -2 for max-price causes a validation error during VM creation.

3. Final Answer:

   max-price cannot be negative; it causes an error. -> Option A

4. Quick Check:

   max-price < -1 = error [OK]

Hint: max-price must be >= -1 [OK]

Common Mistakes:

• Using negative max-price values
• Thinking Spot priority syntax is wrong
• Assuming UbuntuLTS is unsupported

5. You want to run a batch job that can pause and resume without losing progress. Which Spot VM configuration helps minimize cost while ensuring the job restarts automatically if evicted?

hard

A. Set VM priority to Spot, max-price to a low value, and enable automatic redeployment.

B. Use regular VMs with high priority and no max-price limit.

C. Set VM priority to Spot with max-price set to -1 to avoid eviction.

D. Use Spot VMs without max-price and disable automatic redeployment.

Solution

1. Step 1: Choose Spot VM with cost control

   Setting priority to Spot and max-price low saves cost but risks eviction.

2. Step 2: Enable automatic redeployment

   Automatic redeployment restarts the VM if evicted, ensuring job resumes.

3. Final Answer:

   Set VM priority to Spot, max-price to a low value, and enable automatic redeployment. -> Option A

4. Quick Check:

   Spot + max-price + auto redeploy = cost saving + restart [OK]

Hint: Spot + low max-price + auto redeploy = cost + restart [OK]

Common Mistakes:

• Using negative max-price to avoid eviction
• Disabling automatic redeployment
• Choosing regular VMs for cost savings