website/content/en/docs/tasks/configure-pod-container/configure-runasusername.md

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Configure RunAsUserName for Windows pods and containers	templates/task	20

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{{< feature-state for_k8s_version="v1.16" state="alpha" >}}

This page shows how to enable and use the RunAsUserName feature for pods and containers that will run on Windows nodes. This feature is meant to be the Windows equivalent of the Linux-specific runAsUser feature, allowing users to run the container entrypoints with a different username that their default ones.

{{< note >}} Currently this feature is in alpha state. The overall functionality of the feature will not change, but there may be some changes regarding the username validation. Please take this into consideration when testing or adopting this feature. {{< /note >}}

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You need to have a Kubernetes cluster and the kubectl command-line tool must be configured to communicate with your cluster. The cluster is expected to have Windows worker nodes where pods with containers running Windows workloads will get scheduled.

Enable the WindowsRunAsUserName feature gate

In the alpha state, the WindowsRunAsUserName feature gate needs to be enabled on the kube-apiserver service. Without it, the runAsUserName field will be dropped from the pod's, container's, and init container's SecurityContexts. See Feature Gates for an explanation of enabling feature gates. Please make sure feature-gates=WindowsRunAsUserName=true parameter exists in the kube-apiserver command line.

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Set the Username for a Pod

To specify the username with which to execute the Pod's container processes, include the securityContext field ([PodSecurityContext](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#podsecuritycontext-v1-core) in the Pod specification, and within it, the windowsOptions ([WindowsSecurityContextOptions](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#windowssecuritycontextoptions-v1-core) field containing the runAsUserName field.

The Windows security context options that you specify for a Pod apply to all Containers and init Containers in the Pod.

Here is a configuration file for a Windows Pod that has the runAsUserName field set:

{{< codenew file="windows/run-as-username-pod.yaml" >}}

Create the Pod:

kubectl apply -f https://k8s.io/examples/windows/run-as-username-pod.yaml

Verify that the Pod's Container is running:

kubectl get pod run-as-username-pod-demo

Get a shell to the running Container:

kubectl exec -it run-as-username-pod-demo -- powershell

Check that the shell is running user the correct username:

echo $env:USERNAME

The output should be:

ContainerUser

Set the Username for a Container

To specify the username with which to execute a Container's processes, include the securityContext field ([SecurityContext](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#securitycontext-v1-core)) in the Container manifest, and within it, the windowsOptions ([WindowsSecurityContextOptions](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#windowssecuritycontextoptions-v1-core) field containing the runAsUserName field.

The Windows security context options that you specify for a Container apply only to that individual Container, and they override the settings made at the Pod level.

Here is the configuration file for a Pod that has one Container, and the runAsUserName field is set at the Pod level and the Container level:

{{< codenew file="windows/run-as-username-container.yaml" >}}

Create the Pod:

kubectl apply -f https://k8s.io/examples/windows/run-as-username-container.yaml

Verify that the Pod's Container is running:

kubectl get pod run-as-username-container-demo

Get a shell to the running Container:

kubectl exec -it run-as-username-container-demo -- powershell

Check that the shell is running user the correct username (the one set at the Container level):

echo $env:USERNAME

The output should be:

ContainerAdministrator

Windows Username limitations

In order to use this feature, the value set in the runAsUserName field must be a valid username. It must have the following format: DOMAIN\USER, where DOMAIN\ is optional. Windows user names are case insensitive. Additionally, there are some restrictions regarding the DOMAIN and USER:

• The runAsUserName field cannot be empty, and it cannot contain control characters (ASCII values: 0x00-0x1F, 0x7F)
• The DOMAIN must be either a NetBios name, or a DNS name, each with their own restrictions:
  • NetBios names: maximum 15 characters, cannot start with . (dot), and cannot contain the following characters: \ / : * ? " < > |
  • DNS names: maximum 255 characters, contains only alphanumeric characters, dots, and dashes, and it cannot start or end with a . (dot) or - (dash).
• The USER must have at most 20 characters, it cannot contain only dots or spaces, and it cannot contain the following characters: " / \ [ ] : ; | = , + * ? < > @.

Examples of acceptable values for the runAsUserName field: ContainerAdministrator, ContainerUser, NT AUTHORITY\NETWORK SERVICE, NT AUTHORITY\LOCAL SERVICE.

For more information about these limtations, check here and here.

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• Guide for scheduling Windows containers in Kubernetes
• Managing Workload Identity with Group Managed Service Accounts (GMSA)
• Configure GMSA for Windows pods and containers

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