Running Preemptible VMs

This page provides an overview of preemptible VMs support in Google Kubernetes Engine.

Overview

Preemptible VMs are Google Compute Engine VM instances that last a maximum of 24 hours and provide no availability guarantees. Preemptible VMs are priced lower than standard Compute Engine VMs and offer the same machine types and options.

You can use preemptible VMs in your GKE clusters or node pools to run batch or fault-tolerant jobs that are less sensitive to the ephemeral, non-guaranteed nature of preemptible VMs.

To learn more about preemptible VMs, refer to Preemptible VMs in the Compute Engine documentation.

How preemptible VMs work

When GKE clusters or node pools create Compute Engine VMs, the VMs behave like a managed instance group. Preemptible VMs in GKE are subject to the same limitations as preemptible instances in a managed instance group. Preemptible instances terminate after 30 seconds upon receiving a preemption notice.

Additionally, these preemptible VMs are given a Kubernetes label, cloud.google.com/gke-preemptible=true. Kubernetes labels can be used in the nodeSelector field for scheduling Pods to specific nodes.

Here is an example selector for filtering preemptible VMs:

apiVersion: v1
kind: Pod
spec:
  nodeSelector:
    cloud.google.com/gke-preemptible: "true"

Best practices

Because preemptible VMs have no availability guarantees, you should design your system under the assumption that any or all of your Compute Engine instances might be preempted and become unavailable. There are no guarantees as to when new instances become available.

Moreover, there is no guarantee that Pods running on preemptible VMs can always shutdown gracefully.

If you want to ensure that your jobs or workloads are processed even if no preemptible VMs are available, you can create both non-preemptible and preemptible node pools in your cluster.

Creating a cluster or node pool with preemptible VMs

You can use the gcloud command-line tool or GCP Console to create a cluster or node pool with preemptible VMs.

gcloud

You can create a cluster or node pool with preemptible VMs by specifying the --preemptible flag.

To create a cluster with preemptible VMs, run the following command:

gcloud beta container clusters create [CLUSTER_NAME] --preemptible \
[--zone [COMPUTE_ZONE] --project [PROJECT_ID]]

where [COMPUTE_ZONE] is the cluster's compute zone.

To create a node pool with preemptible VMs:

gcloud beta container node-pools create [POOL_NAME] --preemptible \
--cluster [CLUSTER_NAME] [--zone [COMPUTE_ZONE] --project [PROJECT_ID]]

Console

  1. Visit the Google Kubernetes Engine menu in GCP Console.

    Visit the Google Kubernetes Engine menu

  2. Click Create cluster.

  3. Choose the Standard cluster template or choose an appropriate template for your workload.
  4. Configure your cluster as desired. Then, click Advanced edit for the node pool you want to configure.
  5. In the Preemptible nodes section, select Enable preemptible nodes.
  6. Click Save to close the node pool modification overlay.
  7. Click Create.

Using node taints to avoid scheduling to preemptible VM nodes

Depending on your use case, you might want to avoid having critical Pods scheduled on a preemptible VM node. In such cases, you can use a node taint and toleration to avoid scheduling Pods to nodes with preemptible VMs.

Tainting a node for preemptible VMs

To add a node taint for a node with preemptible VMs, run the following command:

kubectl taint nodes [NODE_NAME] cloud.google.com/gke-preemptible="true":NoSchedule

Now, only Pods that tolerate the node taint are scheduled to the node.

Adding toleration to Pods

To add the relevant toleration to your Pods, add the following to your Pod's specification or your object's Pod template specification:

tolerations:
- key: cloud.google.com/gke-preemptible
  operator: Equal
  value: "true"
  effect: NoSchedule

What's next

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