Google Cloud has always had a knack for non-standard virtual machines, and their option of creating Google preemptible VMs is no different. Traditional virtual machines are long-running servers with standard operating systems that are only shut down when you say they can be shut down. On the other hand, preemptible VMs last no longer than 24 hours and can be stopped on a moment’s notice (and may not be available at all). So why use them?

Google Cloud Preemptible VM Overview

Preemptible VMs are designed to be a low-cost, short-duration option for batch jobs and fault-tolerant workloads. Essentially, Google is offering up extra capacity at a huge discount – with the tradeoff that if that capacity is needed for other (full-priced)  resources, your instances can be terminated or “preempted”. Of course, if you’re using them for batch processing, being preempted will slow down your job without completely stopping it. 

You can create your preemptible VMs in a managed instance group in order to easily manage a collection of VMs as a single entity – and, if a VM is preempted, the VM will be automatically recreated. Alternatively, you can use Kubernetes Engine container clusters to automatically recreate preempted VMs.  

Preemptible VM Pricing

Pricing is fixed, not variable, and you can view the preemptible price alongside the on demand prices in Google’s compute pricing list and/or pricing calculator. Prices are 70-80% off on demand, and upward of 50% off even compared to a 3-year committed use discount

Google does not charge you for instances if they are preempted in the first minute after they start running.

Note: Google Cloud Free Tier credits for Compute Engine do not apply to preemptible instances. 

Use Cases for Google Preemptible VMs

As with most trade-offs, the biggest reason to use a preemptible VM is cost. Preemptible VMs can save you up to 80% compared to a normal on-demand virtual machine. (By the way – AWS users will want to use Spot Instances for the same reason, and Azure users can check out Low Priority VMs). This is a huge savings if the workload you’re trying to run consists of short-lived processes or things that are not urgent and can be done any time. This can include things like financial modeling, rendering and encoding, and even some parts of your CI/CD pipeline or code testing framework.

How to Create a Google Preemptible VM

To create a preemptible VM, you can use the Google Cloud Platform console, the ‘gcloud’ command line tool, or the Google Cloud API. The process is the same as creating a standard VM: you select your instance size, networking options, disk setup, and SSH keys, with the one minor change that you enable the ‘preemptible’ flag during setup. The other change you’ll want to make is to create a shutdown script to decide what happens to your processes and data if the instance is stopped without your knowledge. This script can even perform different actions if the instance was preempted as opposed to shut down from something you did.

One nice benefit of Google preemptible VMs is the ability to attach local SSD drives and GPUs to the instances. This means you can get added extensibility and performance for the workload that you are running, while still saving money. You can also have preemptible instances in a managed instance group for high scalability when the instances are available. This can help you process more of your jobs at once when the preemptible virtual machines are able to run.

FAQs About Google Preemptible Instances

How long do GCP preemptible VMs last?

These instances can last up to 24 hours. If you stop or start an instance, the 24-hour counter is reset because the instance transitions into a terminated state. If an instance is reset or other actions that keep it in a running state, the 24-hour clock is not reset. 

Is pricing variable?

No, pricing for preemptible VMs is fixed, so you know in advance what you will pay.

What happens when my instance is preempted? 

When your instance is preempted, you will get a 30 second graceful shutdown period. The instance will get a preemption notice in the form of an ACPI G2 Soft Off signal. You can use a shutdown script to complete cleanup actions before the instance stops. If an instance does not stop after 30 seconds, it will get an ACPI G3 Mechanical Off signal to the operating system, and terminate it. You can practice what this looks like by stopping the instance.

By using managed instance groups, you can automatically recreate your instances if capacity is available. 

How often are you actually preempted?

Google reports an average preemption rate from 5-15% per day per project, with occasional spikes depending on time and zone. This is not a guarantee, though, and you can be preempted at any time. 

How does Google choose which instances to preempt?

Google avoids preempting too many instances from a single customer, and preempts new instances over older instances whenever possible – this is to avoid losing work across your cluster. 

How to Use Google Preemptible VMs to Optimize Costs

Our customers who have the most cost-effective use of Google resources often mix Google preemptible VMs with other instance types based on the workloads. For instance, production systems that need to be up 24/7 can buy committed-use discounts for up to 57% savings on those servers. Non-production systems, like dev, test, QA, and staging, can use on-demand resources with schedules managed by ParkMyCloud to save 65%. Then, any batch workloads or non-urgent jobs can use Google preemptible instances to run whenever available for up to 80% savings. Questions about optimizing cloud costs? We’re happy to help – email us or use the chat client on this page (staffed by real people, including me!).

Further reading on Google Cloud cost optimization:

About Chris Parlette

Chris Parlette is the Director of Cloud Solutions at ParkMyCloud. Chris helps customers reduce their cloud waste and manage their hybrid infrastructures by drawing on his years of experience working at various software startups. From SaaS to on-prem, virtualization to cloud, monitoring tools to cloud management platforms, and small businesses to large enterprises, Chris has seen it all and loves helping drive improvements to IT management. Chris earned a BS in Computer Science from the University of Maryland. He and his wife, Megan, reside in Silver Spring, MD.