Why Spot VMs for cost savings in Azure? - Purpose & Use Cases

The Big Idea

What if you could cut your cloud VM costs by up to 90% without lifting a finger?

The Scenario

Imagine you need to run many virtual machines (VMs) for a project, but you have a tight budget. You try to start regular VMs one by one, paying full price for each, and it quickly becomes expensive.

The Problem

Manually managing VMs at full price means you pay more than necessary. You also waste time checking prices and turning off VMs when costs rise. This slow, error-prone process can blow your budget fast.

The Solution

Spot VMs let you use spare cloud capacity at a big discount. Azure automatically offers these cheaper VMs but may stop them if the capacity is needed elsewhere. This way, you save money without constant manual checks.

Before vs After

✗ Before

Create VM with standard pricing
Start VM
Monitor costs manually

✓ After

Create Spot VM with max price
Start VM
Azure manages interruptions and cost savings

What It Enables

Spot VMs enable you to run large workloads cheaply by using unused cloud capacity automatically.

Real Life Example

A data scientist runs many experiments overnight using Spot VMs, saving up to 90% on costs compared to regular VMs, and finishes work faster without extra budget.

Key Takeaways

Manual VM use can be costly and slow to manage.

Spot VMs offer automatic, discounted access to spare cloud capacity.

This saves money and lets you run bigger workloads efficiently.

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