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Google Cloud Platform: How Preemptible Instances Can Bolster Your Cloud Cost-Optimization Strategy

Back in August last year, Google Cloud Platform announced price reductions of up to 33% on its Preemptible Virtual Machines (VMs), which could deliver potential savings of up to 80% on the cost of its regular on-demand instances.

The move was just the latest in a long series of price cuts designed to attract more enterprise customers to the platform and challenge the dominance of Amazon and Microsoft in the cloud infrastructure marketplace.

But what exactly are Preemptible VMs? And what applications are suitable for deployment to the service? In this post, we run through the main features of Preemptible VMs and compare them with Amazon’s rival discount offering Spot Instances.

What Are Preemptible VMs?

Launched in May 2015, Preemptible VMs are a disposable class of instances through which Google offers excess compute capacity at a much lower price compared with its standard machines.

They’re just like their regular VM counterparts, except that they automatically shut down after 24 hours. What’s more, at any time during that period, they may be shut down at short notice whenever the vendor needs to reclaim spare capacity to meet compute demands elsewhere.

Google takes a number of factors into consideration in its preemption process. For example, it avoids stopping too many VMs from a single customer and gives preference to instances that have been running longer. In other words, instances are more at risk of preemption when they first start running. However, apart from any separate licensing costs, you’re not charged if Google stops your instance within the first 10 minutes.

Charges for Preemptible VMs are typically around 20% of the full on-demand price. Based on average usage, which takes into account partial sustained-use discounts, they generally work out at about 25% of the running cost of the equivalent standard machine. The service carries no guarantee of availability and no SLA.

What Applications Are a Good Fit?

Preemptible VMs are a great way to reduce the cost of processing large-scale workloads that aren’t time sensitive and require massive amounts of compute resources. They’re well suited to security testing, short-term scaling, media encoding, financial or scientific analysis and insurance risk management, where you can spin up hundreds or thousands of machines and quickly complete a job in a short space of time.

They’re a particularly useful option as part of the VM mix for massively parallel processing applications, such as Hadoop and Spark, as they can complement Google’s conventional VMs to enhance performance. However, they’re not suitable for mission-critical services such as operational databases and Internet applications.

How Should Your Workloads Handle Preemption?

First of all, if you haven’t done so already, you should build fault tolerance into your application. You can also mitigate against the impact of preemption by combining regular instances with Preemptible VMs in your clusters, thereby ensuring you maintain a baseline level of compute availability.

Alternatively, you can create a shutdown script that responds to preemption alerts by automatically launching regular instances to cover your shortfall in compute capacity. But, if costs are paramount and you’re prepared to wait, your script should simply clean up and save your job so it can pick up where it left off.

In either case, you should test your application’s response to a preemption event. You can do this by stopping the VM and checking that your script correctly completes your shutdown procedure.

However, if you want to avoid preemption in the first place, you should look to run your instances at off-peak times, such as nights and weekends, when the risk of disruption is at a minimum.

How Do They Compare with Spot Instances?

Preemptible VMs are very similar to Amazon’s Spot Instances. Nevertheless, there are several key differences between them.

Preemptible VMs are charged at fixed rates, which are individually set according to the type and size of instance. Availability depends on the vendor’s level of spare capacity.

By contrast, allocation of Spot Instances is based on a bidding process, where your machine will run as long as your bid price is above the current Spot price on the Spot Market. Provided you don’t cancel your request, the machine will restart whenever the Spot price falls below your bid price. And while your machine is running the actual price you pay is the Spot price.

Some enterprise customers will prefer the more predictable costs of Preemptible VMs. On the other hand, some will like the flexibility of Spot Instances—through the fact they don’t automatically terminate after 24 hours and that you can bid at a higher price to reduce the risk of interruption.

Preemptible VM costs are rounded up to the nearest minute. However, if you terminate your instance within the first 10 minutes, usage is rounded up to a full 10 minutes. By contrast, the costs for Spot Instances are rounded up to the nearest hour. But, if your Spot Instance is interrupted, you don’t pay for your last partial hour of usage.

Finally, Google only gives you 30 seconds’ notice of preemption, while Amazon gives you 2 minutes’ notice of interruption. And Preemptible VMs are available to any Compute Engine instance type, whereas Spot Instances aren’t available to the burstable T2 family of instances.

As yet, there is no Microsoft equivalent of either service.

A Highly Capable Offering

Google is a relative newcomer to the cloud computing arena and still playing catch-up with Amazon and Microsoft in terms of available features and market share. Nevertheless, it has already established itself as a highly capable offering and an ideal cloud platform for specific use cases.

However, in the company’s drive to attract new enterprise customers, pricing will continue to play an important role in its marketing strategy. So, if your applications are a good fit for the platform, you can expect further cost-cutting campaigns and even better value for money from your cloud infrastructure expenditure. And all the more so if you optimize your costs, adopt a flexible approach to your workloads and take advantage of cost-saving options such as Preemptible VMs.