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Windows

Overview

If you need a Windows environment as part of a Tekton Task or Pipeline, you can include Windows container images in your Task steps. Because Windows containers can only run on a Windows host, you will need to have Windows nodes available in your Kubernetes cluster. You should read Windows support in Kubernetes to understand the functionality and limitations of Kubernetes on Windows.

Some important things to note about Windows containers and Kubernetes:

  • Windows containers cannot run on a Linux host.
  • Kubernetes does not support Windows only clusters. The Kubernetes control plane components can only run on Linux.
  • Kubernetes currently only supports process isolated containers, which means a container's base image OS version must match that of the host OS. See Windows container version compatibility for more information.
  • A Kubernetes Pod cannot contain both Windows and Linux containers.

Some important things to note about Windows support in Tekton:

  • A Task can only have Windows or Linux containers, but not both.
  • A Pipeline can contain both Windows and Linux Tasks.
  • In a mixed-OS cluster, TaskRuns and PipelineRuns will need to be scheduled to the correct node using one of the methods described below.
  • Tekton's controller components can only run on Linux nodes.

Scheduling Tasks on Windows Nodes

In order to ensure that Tasks are scheduled to a node with the correct host OS, you will need to update the TaskRun or PipelineRun spec with rules to define this behaviour. This can be done in a couple of different ways, but the simplest option is to specify a node selector.

Node Selectors

Node selectors are the simplest way to schedule pods to a Windows or Linux node. By default, Kubernetes nodes include a label kubernetes.io/os to identify the host OS. The Kubelet populates this with runtime.GOOS as defined by Go. Use spec.podTemplate.nodeSelector (or spec.taskRunSpecs[i].taskPodTemplate.nodeSelector in a PipelineRun) to schedule Tasks to a node with a specific label and value.

For example:

apiVersion: tekton.dev/v1beta1
kind: TaskRun
metadata:
  name: windows-taskrun
spec:
  taskRef:
    name: windows-task
  podTemplate:
    nodeSelector:
      kubernetes.io/os: windows
---
apiVersion: tekton.dev/v1beta1
kind: TaskRun
metadata:
  name: linux-taskrun
spec:
  taskRef:
    name: linux-task
  podTemplate:
    nodeSelector:
      kubernetes.io/os: linux

Node Affinity

Node affinity can be used as an alternative method of defining the OS requirement of a Task. These rules can be set under spec.podTemplate.affinity.nodeAffinity in a TaskRun definition. The example below produces the same result as the previous example which used node selectors.

For example:

apiVersion: tekton.dev/v1beta1
kind: TaskRun
metadata:
  name: windows-taskrun
spec:
  taskRef:
    name: windows-task
  podTemplate:
    affinity:
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
              - matchExpressions:
                - key: kubernetes.io/os
                  operator: In
                  values:
                  - windows
---
apiVersion: tekton.dev/v1beta1
kind: TaskRun
metadata:
  name: linux-taskrun
spec:
  taskRef:
    name: linux-task
  podTemplate:
    affinity:
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
              - matchExpressions:
                - key: kubernetes.io/os
                  operator: In
                  values:
                  - linux