Spot VMs for cost savings in Azure - Deep Dive

Overview - Spot VMs for cost savings

What is it?

Spot VMs are special virtual machines offered by Azure at a lower price because they use unused capacity. They can be interrupted by Azure when the capacity is needed elsewhere. This makes them great for workloads that can handle sudden stops or delays. Spot VMs help save money by using spare resources efficiently.

Why it matters

Without Spot VMs, users would pay full price for virtual machines even when there is spare capacity in the cloud. This means higher costs for running flexible or temporary workloads. Spot VMs allow businesses to reduce cloud expenses significantly by using cheaper, interruptible resources. This helps companies save money and use cloud resources more sustainably.

Where it fits

Before learning about Spot VMs, you should understand basic Azure virtual machines and cloud pricing models. After Spot VMs, you can explore Azure scale sets and workload automation to handle interruptions gracefully. This topic fits into cost optimization and cloud resource management.

Mental Model

Core Idea

Spot VMs are like renting a car that can be taken back anytime but costs much less while you use it.

Think of it like...

Imagine you want to rent a bike from a shop that has extra bikes not currently in use. They rent these bikes cheaply but can ask for them back anytime if a regular customer arrives. You save money but must be ready to stop using the bike quickly.

┌───────────────┐       ┌───────────────┐
│ Azure Cloud   │       │ User Workload │
│ Unused       │──────▶│ Runs on Spot  │
│ Capacity     │       │ VM at low cost│
└───────────────┘       └───────────────┘
         ▲                      │
         │ Interrupts when      │
         │ capacity needed      │
         └─────────────────────┘

Build-Up - 7 Steps

1

Foundation

What are Azure Virtual Machines

Concept: Introduce the basic idea of virtual machines in Azure as computers in the cloud.

Azure Virtual Machines (VMs) are like computers you can use over the internet. Instead of buying a physical computer, you rent one from Azure. You can install software, run programs, and store data on these VMs just like on your own PC.

Result

You understand that VMs are cloud computers you rent and control remotely.

Knowing what a VM is helps you grasp how Spot VMs fit as a special kind of these cloud computers.

2

Foundation

Understanding Cloud Pricing Models

Concept: Explain how cloud services charge based on usage and resource types.

Cloud providers charge for VMs based on how long you use them and their size. Regular VMs have fixed prices. Some VMs can be cheaper if they use spare resources but might be less reliable.

Result

You see that cloud costs vary and some options trade reliability for lower price.

Understanding pricing helps you appreciate why Spot VMs exist and when to use them.

3

Intermediate

Introducing Spot VMs and Their Interruptions

🤔Before reading on: do you think Spot VMs run continuously like regular VMs or can they be stopped anytime? Commit to your answer.

Concept: Spot VMs use spare capacity and can be stopped by Azure when needed.

Spot VMs are cheaper because they use leftover cloud capacity. However, Azure can stop them at any time if that capacity is needed for other customers. This interruption means your workload must handle sudden stops.

Result

You learn Spot VMs save money but can be interrupted unexpectedly.

Knowing Spot VMs can be interrupted is key to using them correctly and avoiding data loss.

4

Intermediate

Use Cases Suitable for Spot VMs

🤔Before reading on: do you think Spot VMs are good for critical databases or flexible batch jobs? Commit to your answer.

Concept: Spot VMs are best for workloads that can pause or restart without big problems.

Spot VMs work well for tasks like testing, batch processing, or big data jobs that can stop and resume. They are not good for critical apps that must always run without interruption.

Result

You can identify when to choose Spot VMs to save costs safely.

Matching workload type to Spot VM characteristics prevents costly downtime.

5

Intermediate

How to Request and Configure Spot VMs

Concept: Explain how to create Spot VMs in Azure and set eviction policies.

When creating a VM in Azure, you select the Spot VM option. You also choose eviction policies: 'Deallocate' (stop VM but keep data) or 'Delete' (remove VM and data). This controls what happens when Azure interrupts the VM.

Result

You know how to set up Spot VMs and control their behavior on interruption.

Configuring eviction policies helps balance cost savings with data safety.

6

Advanced

Handling Spot VM Interruptions Gracefully

🤔Before reading on: do you think your app should save state frequently or can ignore interruptions? Commit to your answer.

Concept: Teach strategies to make workloads resilient to Spot VM interruptions.

To use Spot VMs well, design apps to save progress often, use checkpoints, or restart tasks automatically. Azure also provides eviction notices a few minutes before stopping the VM, which you can use to prepare.

Result

Your workloads can continue smoothly despite Spot VM interruptions.

Handling interruptions properly unlocks the full cost-saving potential of Spot VMs.

7

Expert

Spot VMs in Azure Scale Sets for Auto Scaling

🤔Before reading on: do you think Spot VMs can be combined with regular VMs in scale sets? Commit to your answer.

Concept: Explain how Spot VMs integrate with scale sets to balance cost and reliability.

Azure Scale Sets can mix Spot VMs with regular VMs. This lets you run most workloads on cheap Spot VMs and fall back on regular VMs when Spot capacity is unavailable. The scale set manages VM counts automatically.

Result

You can build scalable, cost-efficient systems using Spot VMs and regular VMs together.

Combining Spot and regular VMs in scale sets provides a practical balance of cost savings and uptime.

Under the Hood

Azure tracks unused physical servers and offers their capacity as Spot VMs at a discount. When demand rises, Azure interrupts Spot VMs by either deallocating or deleting them based on your eviction policy. Azure sends a short eviction notice before stopping the VM, allowing some cleanup. This system maximizes hardware use while protecting paying customers with regular VMs.

Why designed this way?

Spot VMs were created to use idle cloud capacity efficiently and reduce waste. The tradeoff is that these VMs can be interrupted, which is acceptable for flexible workloads. Alternatives like reserved or on-demand VMs guarantee uptime but cost more. This design balances cost savings with reliability.

┌───────────────┐       ┌───────────────┐       ┌───────────────┐
│ Azure Data    │       │ Spot VM User  │       │ Azure Control │
│ Center       │──────▶│ Runs Workload │◀──────│ Plane Monitors│
│ Physical     │       │               │       │ Capacity &    │
│ Servers      │       │               │       │ Interruptions │
└───────────────┘       └───────────────┘       └───────────────┘
         ▲                      │                      ▲
         │                      │ Eviction Notice      │
         └──────────────────────┴──────────────────────┘

Myth Busters - 4 Common Misconceptions

Quick: Do Spot VMs guarantee your workload will never be interrupted? Commit to yes or no.

Common Belief: Spot VMs run like regular VMs without interruptions.

Reality: Spot VMs can be stopped by Azure at any time when capacity is needed elsewhere.

Why it matters: Assuming Spot VMs are stable can cause data loss or downtime if your app is not designed for interruptions.

Quick: Can you use Spot VMs for critical databases that must always be available? Commit to yes or no.

Common Belief: Spot VMs are suitable for all types of workloads, including critical ones.

Reality: Spot VMs are best for flexible, interruptible workloads, not critical always-on services.

Why it matters: Using Spot VMs for critical apps risks unexpected outages and data corruption.

Quick: Do you think eviction means your data is always deleted? Commit to yes or no.

Common Belief: When a Spot VM is evicted, all data is lost automatically.

Reality: Eviction can either deallocate (stop VM but keep data) or delete VM and data, depending on your eviction policy.

Why it matters: Misunderstanding eviction policies can lead to accidental data loss or unnecessary downtime.

Quick: Do you think Spot VMs always cost less than reserved VMs? Commit to yes or no.

Common Belief: Spot VMs are always the cheapest option compared to reserved or on-demand VMs.

Reality: Spot VM prices vary and can sometimes be higher than reserved VMs, especially if demand for spare capacity is low.

Why it matters: Assuming Spot VMs are always cheapest can lead to unexpected costs or poor budgeting.

Expert Zone

1

Spot VM eviction notices provide a short window (usually 30 seconds) to prepare workloads, but this is often too brief for complex cleanup.

2

Combining Spot VMs with regular VMs in scale sets allows automatic fallback, but requires careful capacity and cost management to avoid surprises.

3

Spot VM availability varies by region and VM size, so planning must consider geographic and SKU-specific capacity fluctuations.

When NOT to use

Avoid Spot VMs for critical, stateful, or latency-sensitive applications that require guaranteed uptime. Use reserved or on-demand VMs instead. For workloads needing high availability, consider combining Spot VMs with regular VMs in scale sets.

Production Patterns

In production, Spot VMs are often used for batch processing, testing environments, big data analytics, and CI/CD pipelines. Teams automate checkpointing and use scale sets to mix Spot and regular VMs, balancing cost and reliability dynamically.

Connections

Preemptible VMs in Google Cloud

Similar concept offering low-cost, interruptible VMs in another cloud provider.

Understanding Spot VMs helps grasp how different clouds optimize unused capacity with interruptible instances.

Interruptible Jobs in Batch Processing

Spot VMs are ideal for workloads designed as interruptible batch jobs.

Knowing batch job design principles aids in effectively using Spot VMs for cost savings.

Airline Overbooking Strategy

Both use spare capacity with risk of interruption or denial of service.

Spot VMs and airline overbooking show how managing spare resources involves balancing cost savings with risk of disruption.

Common Pitfalls

#1 Running critical applications on Spot VMs without interruption handling.

Wrong approach:

Deploy a production database on a Spot VM without backup or failover.

Correct approach:

Use regular VMs or combine Spot VMs with regular VMs and implement failover for critical databases.

Root cause:

Misunderstanding that Spot VMs can be interrupted anytime leads to risky deployments.

#2 Ignoring eviction policies and data persistence options.

Wrong approach:

Create Spot VMs with eviction policy set to 'Delete' but expect data to persist after eviction.

Correct approach:

Set eviction policy to 'Deallocate' if you want to keep data and handle interruptions gracefully.

Root cause:

Not configuring eviction policies properly causes unexpected data loss.

#3 Assuming Spot VM availability is constant across regions and VM sizes.

Wrong approach:

Choose any VM size and region for Spot VMs without checking capacity availability.

Correct approach:

Check Spot VM availability and pricing per region and VM size before deployment.

Root cause:

Overlooking capacity variability leads to deployment failures or higher costs.

Key Takeaways

Spot VMs offer significant cost savings by using Azure's unused capacity but can be interrupted anytime.

They are best suited for flexible, interruptible workloads like batch jobs, testing, and analytics.

Proper configuration of eviction policies and interruption handling is essential to avoid data loss.

Combining Spot VMs with regular VMs in scale sets balances cost savings with reliability in production.

Understanding Spot VM availability and pricing variability helps plan effective and cost-efficient deployments.