Compute Engine provides idle VM recommendations to help you identifyvirtual machine (VM) instances that have not been used over the previous 1 to14 days. You can use idle VM recommendations to find and stop idle VM instancesto reduce wasting resources and reduce your compute bill.

Compute Engine generates recommendations automatically based on systemmetrics gathered by the Cloud Monitoring service. You can configure idle VMrecommendations to receive more or fewer recommendations.

This page provides conceptual information on how Compute Engine generatesidle VM recommendations and on the parameters you can use to configure them.

• For more information on how to identify idle VMs and take action, seeView and apply idle VM recommendations.
• For more information on how to configure idle VM recommendations, seeConfigure idle VM recommendations.

Pricing

Idle VM recommendations are available free of charge. Using recommendationsto reduce your resource usage can result in cost savings.

Limitations

For standalone VMs, idle VM recommendations are not available in following cases:

• Instances with local SSDs
• Instances with GPU/TPUs
• App Engine flex resources
• Dataflow resources
• Google Kubernetes Engine resources

How detection of idle VM instances works

Compute Engine generates recommendations about idle VM instances basedon historical usage metrics. By default, the historical observation period is14 days, or, for new VMs, starting one day after VM creation.By changing the default observation period, you can customize therecommendations that you receive.

To generate recommendations, the algorithm considers the CPU and network usagein the last observation period.If CPU and network usage are below predefined thresholds,the Recommender classifies the VM as idle.

Machine type sizing recommendations recommend the optimal size for a VM. You might receive a machine typerecommendation to downsize an idle VM.

If you must keep an idle VM running despite its low utilization, you can usemachine type recommendations to help you choose the optimal size forunderutilized VMs.

Customize recommendations

This product or feature is subject to the "Pre-GA Offerings Terms" in the General Service Terms section of theService Specific Terms. Pre-GA products and features are available "as is" and might have limited support. For more information, see thelaunch stage descriptions.

Compute Engine lets you customize the recommendations you receive foryour project by changing the configuration used by the recommendation algorithm.In particular, by changing the default observation period, you can receiverecommendations that better fit your workloads, applications,and infrastructure needs.

To learn how to modify the configuration for your project,seeConfigure idle VM recommendations.

Choose the right configuration

This section describes the values that you can set for the configuration.Changing these values affects the recommendations that you receive.

The observation period

Set the observation period to modify the duration of the window used tocalculate the recommendations.

You can set the observation period to a value between 1 day and 14 days, usinga string with the total number of seconds, followed by the letters.

• For an observation period of 1 day, use"86400s".
• For an observation period of 14 days, use"1209600s".

By default, the observation period is 14 days.

• Use a shorter observation period if you want to receive recommendationsbased on short-term changes in your workload.
• Use a longer observation period if you want to receive recommendationsthat are not affected by short-term fluctuations in your workload.

What's next

• Learn how toview and apply idle VM recommendations.
• Learn how toconfigure idle VM recommendations.