Preemptible and Spot VMs in GCP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Preemptible VM in Google Cloud?

A Preemptible VM is a virtual machine that runs at a lower cost but can be stopped by Google Cloud at any time, usually within 24 hours. It's good for short, fault-tolerant tasks.

intermediate

How does a Spot VM differ from a Preemptible VM?

Spot VMs are similar to Preemptible VMs but offer more flexible pricing and availability. They can be interrupted but may run longer and have different pricing models.

beginner

Why would you choose a Preemptible or Spot VM over a regular VM?

Because they cost less, making them ideal for batch jobs, testing, or workloads that can handle interruptions without losing important data.

intermediate

What happens to your data when a Preemptible VM is stopped?

The VM is stopped without warning, and any data stored on the VM's local disk is lost. Persistent disks keep data safe.

advanced

How can you design your application to handle Preemptible VM interruptions?

Use checkpointing, save important data to persistent storage, and design your app to restart or continue work after interruptions.

What is the maximum runtime for a Preemptible VM before it is stopped by Google Cloud?

A 12 hours

B 24 hours

C 48 hours

D No limit

Preemptible VMs can run up to 24 hours before Google Cloud stops them.

Which of the following is a key benefit of using Spot VMs?

A Lower cost with flexible availability

B Guaranteed uptime

C Unlimited runtime

D No interruptions

Spot VMs offer lower cost but can be interrupted, with flexible availability.

What should you use to keep data safe when using Preemptible VMs?

A Persistent disks

B Local VM disk

C Temporary storage

D No storage needed

Persistent disks keep data safe even if the VM is stopped.

Which workload is best suited for Preemptible or Spot VMs?

A Critical database servers

B Real-time user-facing apps

C Batch processing jobs

D Long-running backend services

Batch jobs can handle interruptions and benefit from lower costs.

What is a common strategy to handle VM interruptions?

A Running only on regular VMs

B Ignoring interruptions

C Using only local storage

D Checkpointing and saving state

Checkpointing helps resume work after interruptions.

Explain what Preemptible and Spot VMs are and when to use them.

Think about cheaper VMs that can be stopped anytime.

Describe how to design an application to work well with Preemptible or Spot VMs.

Focus on fault tolerance and data safety.

Practice

1. What is the main advantage of using Preemptible or Spot VMs in Google Cloud?

easy

A. They offer unlimited storage capacity

B. They provide guaranteed uptime for critical applications

C. They cost less but can be stopped at any time

D. They automatically scale without user input

Solution

1. Step 1: Understand the cost and availability trade-off

   Preemptible and Spot VMs are cheaper because Google can stop them anytime to reclaim resources.

2. Step 2: Identify the main benefit

   The main benefit is cost savings with the risk of interruption, not guaranteed uptime or unlimited storage.

3. Final Answer:

   They cost less but can be stopped at any time -> Option C

4. Quick Check:

   Cost savings with interruptions = D [OK]

Hint: Cheaper VMs can be stopped anytime, so cost saving is main benefit [OK]

Common Mistakes:

• Thinking they guarantee uptime
• Assuming they scale automatically
• Confusing with storage features

2. Which of the following is the correct way to specify a Spot VM in a Google Cloud VM creation command?

easy

A. gcloud compute instances create my-vm --spot

B. gcloud compute instances create my-vm --interruptible

C. gcloud compute instances create my-vm --preemptible

D. gcloud compute instances create my-vm --ephemeral

Solution

1. Step 1: Recall the flag for Spot VMs

   Spot VMs use the flag --spot in the gcloud command.

2. Step 2: Differentiate from Preemptible flag

   --preemptible is for older Preemptible VMs, --spot is the newer recommended option.

3. Final Answer:

   gcloud compute instances create my-vm --spot -> Option A

4. Quick Check:

   Spot VM flag = --spot [OK]

Hint: Spot VMs use --spot flag, not --preemptible [OK]

Common Mistakes:

• Using --preemptible for Spot VMs
• Confusing --interruptible as a flag
• Using unrelated flags like --ephemeral

3. Consider this snippet of a VM creation command:
gcloud compute instances create test-vm --zone=us-central1-a --spot --machine-type=e2-medium
What will happen if Google Cloud needs the resources back?

medium

A. The VM will automatically migrate to another zone

B. The VM will continue running without interruption

C. The VM will be stopped immediately without warning

D. The VM will receive a 30-second warning before stopping

Solution

1. Step 1: Understand Spot VM behavior on resource reclamation

   Spot VMs are interruptible but Google Cloud sends a 30-second warning before stopping them.

2. Step 2: Eliminate other options

   Immediate stop without warning is incorrect; automatic migration does not happen for Spot VMs; uninterrupted running contradicts the interruptible nature.

3. Final Answer:

   The VM will receive a 30-second warning before stopping -> Option D

4. Quick Check:

   Spot VMs get 30-second warning before stop = A [OK]

Hint: Spot VMs get 30-second warning before stopping [OK]

Common Mistakes:

• Assuming immediate stop without warning
• Thinking Spot VMs migrate automatically
• Believing Spot VMs never stop

4. You created a VM with the command:
gcloud compute instances create my-vm --preemptible --zone=us-east1-b
But you want to switch to Spot VM instead. What is the correct fix?

medium

A. Add --spot flag without removing --preemptible

B. Replace --preemptible with --spot in the command

C. Change the zone to a Spot-only zone

D. Use --interruptible flag instead of --preemptible

Solution

1. Step 1: Identify the correct flag for Spot VMs

   Spot VMs require the --spot flag, not --preemptible.

2. Step 2: Correct the command by replacing flags

   Remove --preemptible and add --spot to switch VM type.

3. Final Answer:

   Replace --preemptible with --spot in the command -> Option B

4. Quick Check:

   Switching VM type requires flag replacement = B [OK]

Hint: Remove --preemptible, add --spot to switch VM type [OK]

Common Mistakes:

• Adding --spot without removing --preemptible
• Changing zone expecting Spot-only zones
• Using non-existent --interruptible flag

5. You want to run a batch job that can tolerate interruptions and save costs. Which approach best uses Spot VMs to handle sudden stops and restarts?

hard

A. Design the job to save progress frequently and restart automatically on VM preemption

B. Use Spot VMs without any checkpointing or restart logic

C. Run the job on standard VMs to avoid interruptions

D. Use Spot VMs but disable automatic restarts

Solution

1. Step 1: Understand Spot VM interruption nature

   Spot VMs can stop anytime, so jobs must handle interruptions gracefully.

2. Step 2: Choose a strategy to handle interruptions

   Saving progress frequently and restarting automatically ensures job completion despite stops.

3. Step 3: Eliminate unsafe options

   Running without checkpointing risks data loss; standard VMs cost more; disabling restarts loses fault tolerance.

4. Final Answer:

   Design the job to save progress frequently and restart automatically on VM preemption -> Option A

5. Quick Check:

   Checkpointing + auto-restart = reliable Spot VM use [OK]

Hint: Checkpoint progress and auto-restart for Spot VM jobs [OK]

Common Mistakes:

• Ignoring checkpointing and restart logic
• Choosing standard VMs for cost savings
• Disabling automatic restarts on Spot VMs