Preemptible and Spot VMs in GCP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

Behavior of Preemptible VMs on GCP

What happens to a Google Cloud preemptible VM when Google needs the resources back?

A The VM is terminated with a 30-second preemption notice and cannot be restarted.

B The VM is stopped and can be restarted later manually.

C The VM is paused and resumes automatically when resources are free.

D The VM is migrated live to another host without downtime.

💡 Hint

Think about how preemptible VMs are designed for cost savings but with limited availability.

Preemptible VMs are terminated with a 30-second preemption notice when Google reclaims resources. They cannot be restarted and are meant for fault-tolerant workloads.

❓ Architecture

intermediate

Best Use Case for Spot VMs

Which workload is best suited to run on Google Cloud Spot VMs?

A A critical database server requiring high availability.

B A web server handling live user traffic with low latency needs.

C A stateful application storing user session data.

D Batch processing jobs that can be restarted if interrupted.

💡 Hint

Consider the interruption nature of Spot VMs and which workloads tolerate it.

Spot VMs are ideal for batch jobs that can be restarted because they may be interrupted when resources are reclaimed.

❓ security

advanced

Security Implications of Using Preemptible VMs

Which security risk is most relevant when using preemptible VMs in Google Cloud?

A Increased risk of VM hijacking due to longer uptime.

B Data loss due to unexpected VM termination without shutdown.

C Exposure to network attacks because preemptible VMs bypass firewalls.

D Automatic disabling of encryption on preemptible VM disks.

💡 Hint

Think about what happens when a preemptible VM is stopped abruptly.

Because preemptible VMs can be terminated with only a 30-second warning, unsaved data in memory or local disks may be lost, posing a data loss risk.

✅ Best Practice

advanced

Handling Spot VM Interruptions Gracefully

What is the best practice to handle interruptions of Spot VMs in Google Cloud?

A Use a shutdown script to save state and shut down cleanly on interruption notice.

B Disable automatic updates to prevent VM restarts during Spot interruptions.

C Manually monitor VM status and restart interrupted VMs yourself.

D Ignore interruptions since Spot VMs never send warnings before termination.

💡 Hint

Spot VMs provide a short warning before termination. How can you use that?

Spot VMs send a 30-second termination notice. Using a shutdown script to save state allows graceful handling of interruptions.

🧠 Conceptual

expert

Difference Between Preemptible and Spot VMs

Which statement correctly describes a key difference between Google Cloud Preemptible VMs and Spot VMs?

A Spot VMs cannot be used with managed instance groups; Preemptible VMs can.

B Spot VMs are always cheaper than Preemptible VMs and never get interrupted.

C Preemptible VMs have a fixed maximum runtime of 24 hours; Spot VMs do not have a fixed maximum runtime.

D Preemptible VMs support live migration; Spot VMs do not.

💡 Hint

Consider runtime limits and interruption behavior differences.

Preemptible VMs have a maximum runtime of 24 hours and are terminated after that. Spot VMs do not have this fixed limit but can be interrupted anytime.

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