You can schedule Windows workloads to Windows compute nodes.


  • You installed the Windows Machine Config Operator (WMCO) using Operator Lifecycle Manager (OLM).

  • You are using a Windows container as the OS image with the Docker-formatted container runtime add-on enabled.

  • You have created a Windows machine set.

Currently, the Docker-formatted container runtime is used in Windows nodes. Kubernetes is deprecating Docker as a container runtime; you can reference the Kubernetes documentation for more information in Docker deprecation. Containerd will be the new supported container runtime for Windows nodes in a future release of Kubernetes.

Windows pod placement

Before deploying your Windows workloads to the cluster, you must configure your Windows node scheduling so pods are assigned correctly. Since you have a machine hosting your Windows node, it is managed the same as a Linux-based node. Likewise, scheduling a Windows pod to the appropriate Windows node is completed similarly, using mechanisms like taints, tolerations, and node selectors.

With multiple operating systems, and the ability to run multiple Windows OS variants, in the same cluster, you must map your Windows pods to a base Windows OS variant by using a RuntimeClass. For example, if you have multiple Windows nodes running on different Windows Server container versions, the cluster could schedule your Windows pods to an incompatible Windows OS variant. You must have RuntimeClass objects configured for each Windows OS variant on your cluster. Using a RuntimeClass object is also recommended if you have only one Windows OS variant available in your cluster.

For more information, see Microsoft’s documentation on Host and container version compatibility.

Additional resources

Creating a RuntimeClass object to encapsulate scheduling mechanisms

Using a RuntimeClass object simplifies the use of scheduling mechanisms like taints and tolerations; you deploy a runtime class that encapsulates your taints and tolerations and then apply it to your pods to schedule them to the appropriate node. Creating a runtime class is also necessary in clusters that support multiple operating system variants.

  1. Create a RuntimeClass object YAML file. For example, runtime-class.yaml:

    apiVersion: node.k8s.io/v1beta1
    kind: RuntimeClass
      name: <runtime_class_name> (1)
    handler: 'docker'
      nodeSelector: (2)
        kubernetes.io/os: 'windows'
        kubernetes.io/arch: 'amd64'
        node.kubernetes.io/windows-build: '10.0.17763'
      tolerations: (3)
      - effect: NoSchedule
        key: os
        operator: Equal
        value: "Windows"
    1 Specify the RuntimeClass object name, which is defined in the pods you want to be managed by this runtime class.
    2 Specify labels that must be present on nodes that support this runtime class. Pods using this runtime class can only be scheduled to a node matched by this selector. The node selector of the runtime class is merged with the existing node selector of the pod. Any conflicts prevent the pod from being scheduled to the node.
    3 Specify tolerations to append to pods, excluding duplicates, running with this runtime class during admission. This combines the set of nodes tolerated by the pod and the runtime class.
  2. Create the RuntimeClass object:

    $ oc create -f <file-name>.yaml

    For example:

    $ oc create -f runtime-class.yaml
  3. Apply the RuntimeClass object to your pod to ensure it is scheduled to the appropriate operating system variant:

    apiVersion: v1
    kind: Pod
      name: my-windows-pod
      runtimeClassName: <runtime_class_name> (1)
    1 Specify the runtime class to manage the scheduling of your pod.

Sample Windows container workload deployment

You can deploy Windows container workloads to your cluster once you have a Windows compute node available.

This sample deployment is provided for reference only.

Example Service object
apiVersion: v1
kind: Service
  name: win-webserver
    app: win-webserver
    # the port that this service should serve on
  - port: 80
    targetPort: 80
    app: win-webserver
  type: LoadBalancer
Example Deployment object
apiVersion: apps/v1
kind: Deployment
    app: win-webserver
  name: win-webserver
      app: win-webserver
  replicas: 1
        app: win-webserver
      name: win-webserver
      - key: "os"
        value: "Windows"
        Effect: "NoSchedule"
      - name: windowswebserver
        image: mcr.microsoft.com/windows/servercore:ltsc2019
        imagePullPolicy: IfNotPresent
        - powershell.exe
        - -command
        - $listener = New-Object System.Net.HttpListener; $listener.Prefixes.Add('http://*:80/'); $listener.Start();Write-Host('Listening at http://*:80/'); while ($listener.IsListening) { $context = $listener.GetContext(); $response = $context.Response; $content='<html><body><H1>Red Hat OpenShift + Windows Container Workloads</H1></body></html>'; $buffer = [System.Text.Encoding]::UTF8.GetBytes($content); $response.ContentLength64 = $buffer.Length; $response.OutputStream.Write($buffer, 0, $buffer.Length); $response.Close(); };
            runAsUserName: "ContainerAdministrator"
        kubernetes.io/os: windows

When using the mcr.microsoft.com/powershell:<tag> container image, you must define the command as pwsh.exe. If you are using the mcr.microsoft.com/windows/servercore:<tag> container image, you must define the command as powershell.exe. For more information, see Microsoft’s documentation.

Scaling a machine set manually

To add or remove an instance of a machine in a machine set, you can manually scale the machine set.

This guidance is relevant to fully automated, installer-provisioned infrastructure installations. Customized, user-provisioned infrastructure installations do not have machine sets.

  • Install an OKD cluster and the oc command line.

  • Log in to oc as a user with cluster-admin permission.

  1. View the machine sets that are in the cluster:

    $ oc get machinesets -n openshift-machine-api

    The machine sets are listed in the form of <clusterid>-worker-<aws-region-az>.

  2. Scale the machine set:

    $ oc scale --replicas=2 machineset <machineset> -n openshift-machine-api


    $ oc edit machineset <machineset> -n openshift-machine-api

    You can alternatively apply the following YAML to scale the machine set:

    apiVersion: machine.openshift.io/v1beta1
    kind: MachineSet
      name: <machineset>
      namespace: openshift-machine-api
      replicas: 2

    You can scale the machine set up or down. It takes several minutes for the new machines to be available.