Use Active Directory single sign-on for secure connection to Kubernetes API server in AKS hybrid

Applies to: AKS on Azure Stack HCI, AKS on Windows Server

You can create a secure connection to your Kubernetes API server in AKS hybrid using Active Directory (AD) single sign-on (SSO) credentials.

Overview of AD in AKS hybrid

Without Active Directory authentication, users must rely on a certificate-based kubeconfig file when connecting to the API server via the kubectl command. The kubeconfig file contains secrets such as private keys and certificates that need to be carefully distributed, which can be a significant security risk.

As an alternative to using certificate-based kubeconfig, you can use AD SSO credentials as a secure way to connect to the API server. AD integration with AKS hybrid lets users on a Windows domain-joined machine connect to the API server via kubectl using their SSO credentials. This removes the need to manage and distribute certificate-based kubeconfig files that contain private keys.

AD integration uses AD kubeconfig, which is distinct from the certificate-based kubeconfig files and doesn't contain any secrets. However, the certificate-based kubeconfig file can be used for backup purposes, such as troubleshooting, if there are issues with connecting using Active Directory credentials.

Another security benefit with AD integration is that the users and groups are stored as security identifiers (SIDs). Unlike group names, SIDs are immutable and unique and therefore present no naming conflicts.

Note

Currently, AD SSO connectivity is only supported for workload clusters.

This document will guide you through the following steps to set up Active Directory as the identity provider and to enable SSO via kubectl:

  • Create the AD account for the API server, and then create the keytab file associated with the account. See Create AD Auth using the keytab file to create the AD account and generate the keytab file.
  • Use the keytab file to install AD Auth on the Kubernetes cluster. As part of this step, a default role-based access control (RBAC) configuration is automatically created.
  • Convert group names to SIDs and vice-versa when creating or editing RBAC configurations, see create and update the AD group role binding for instructions.

Before you begin

Before you start the process of configuring Active Directory SSO credentials, you should ensure you have the following items available:

  • The latest Aks-Hci PowerShell module is installed. If you need to install it, see download and install the AksHci PowerShell module.

  • The AKS host is installed and configured. If you need to install the host, follow the steps to configure your deployment.

  • The keytab file is available to use. If it isn't available, follow the steps to create the API server AD account and the keytab file.

    Note

    You should generate the keytab file for a specific service principal name (SPN), and this SPN must correspond to the API server AD account for the workload cluster. You must also ensure that the same SPN is used throughout the AD authentication process. The keytab file should be named current.keytab.

  • One API server AD account is available for each AKS workload cluster.

  • The client machine must be a Windows domain-joined machine.

Create AD Auth using the keytab file

Step 1: Create the workload cluster and enable AD authentication

Before you install AD authentication, you must first create an AKS workload cluster and enable the AD authentication add-on on the cluster. If you don't enable AD authentication when you create the new cluster, you can't enable it later.

Open PowerShell as an administrator and run the following using the -enableADAuth parameter of the New-AksHciCluster command:

New-AksHciCluster -name mynewcluster1 -enableADAuth

For each workload cluster, ensure there's one API server AD account available.

For details on creating the workload cluster, see Create Kubernetes clusters using Windows PowerShell.

Step 2: Install AD authentication

Before you can install AD authentication, the workload cluster must be installed and the AD authentication enabled on the cluster. To install AD authentication, use one of the following options.

Option 1

For a domain-joined Azure Stack HCI or Windows Server cluster, open PowerShell as an administrator and run the following command:

Install-AksHciAdAuth -name mynewcluster1 -keytab .\current.keytab -SPN k8s/apiserver@CONTOSO.COM -adminUser contoso\bob

Note

For SPN k8s/apiserver@CONTOSO.com, use the format SPN k8s/apiserver@<realm name>. On first attempt, specify <realm name> in uppercase letters. However, if you are having issues, create the SPN with lowercase letters. Kerberos is case sensitive.

Option 2

If the cluster host isn't domain-joined, use the admin user name or group name in SID format as shown in the following example:

If using an admin user:

Install-AksHciAdAuth -name mynewcluster1 -keytab .\current.keytab -SPN k8s/apiserver@CONTOSO.COM -adminUserSID <User SID>

If using an admin group:

Install-AksHciAdAuth -name mynewcluster1 -keytab .\current.keytab -SPN k8s/apiserver@CONTOSO.COM -adminGroupSID <Group SID>

To find the SID for the user account, see Determine the user or group security identifier.

Before proceeding to the next steps, make note of the following items:

  • Make sure the keytab file is named current.keytab.
  • Replace the SPN that corresponds to your environment.
  • The -adminGroup parameter creates a corresponding role binding for the specified AD group with cluster admin privileges. Replace contoso\bob (as shown in Option 1, above) with the AD group or user that corresponds to your environment.

Step 3: Test the AD webhook and keytab file

You need to make sure the AD webhook is running on the API server and the keytab file is stored as a Kubernetes secret. To get the certificate-based kubeconfig file for the workload cluster, follow these steps:

  1. Get a certificate-based kubeconfig file using the following command. You'll use the kubeconfig file to connect to the cluster as a local host.

    Get-AksHciCredential -name mynewcluster1
    
  2. Run kubectl on the server that you connected to (using the certificate-based kubeconfig file you previously created) and then check the AD webhook deployment to make sure it's in the format ad-auth-webhook-xxxx.

    kubectl get pods -n=kube-system
    
  3. Run kubectl to check that the keytab file is deployed as a secret and is listed as a Kubernetes secret:

    kubectl get secrets -n=kube-system
    

Step 4: Create the AD kubeconfig file

Once the AD webhook and keytab are successfully deployed, create the AD kubeconfig file. After the file is created, copy the AD kubeconfig file to the client machine and use it to authenticate to the API server. Unlike the certificate-based kubeconfig file, AD kubeconfig isn't a secret and is safe to copy as plain text.

Open PowerShell as an administrator and run the following command:

Get-AksHciCredential -name mynewcluster1 -configPath .\AdKubeconfig -adAuth

Step 5: Copy kubeconfig and other files to the client machine

You should copy the three files listed below from the AKS workload cluster to your client machine:

  • Copy the AD kubeconfig file created in the previous step to $env:USERPROFILE.kube\config.

  • Create the folder path c:\adsso and copy the following files from the AKS workload cluster to your client machine.

    • Kubectl.exe under $env:ProgramFiles\AksHci to c:\adsso
    • Kubectl-adsso.exe under $env:ProgramFiles\AksHci to c:\adsso

    Note

    The adsso.exe file is generated on the server when you run the Get-AksHciCredential cmdlet.

Step 6: Connect to the API server from the client machine

After you've completed the previous steps, use your SSO credentials to sign in to your Windows domain-joined client machine. Open PowerShell, and then attempt to access the API server using kubectl. If the operation completes successfully, you have set up AD SSO correctly.

Create and update the AD group role binding

As mentioned in Step 2, a default role binding with cluster admin privileges is created for the user and/or the group that was provided during installation. Role binding in Kubernetes defines the access policies for AD groups. This step describes how to use RBAC to create new AD group role bindings in Kubernetes and to edit existing role bindings. For example, the cluster admin may want to grant additional privileges to users by using AD groups (which makes the process more efficient). To learn more about RBAC, see using RBAC authorization.

When you create or edit other AD group RBAC entries, the subject name should have the "microsoft:activedirectory:CONTOSO\\group name" prefix. Note that the names must contain a domain name and a prefix that are enclosed by double quotes.

Here are two examples:

Example 1

apiVersion: rbac.authorization.k8s.io/v1 
kind: ClusterRoleBinding 
metadata: 
  name: ad-user-cluster-admin 
roleRef: 
  apiGroup: rbac.authorization.k8s.io 
  kind: ClusterRole 
  name: cluster-admin 
subjects: 
- apiGroup: rbac.authorization.k8s.io 
  kind: User 
  name: "microsoft:activedirectory:CONTOSO\Bob" 

Example 2

The example below shows how to create a custom role and role binding for a namespace with an AD group. In the example, "SREGroup" is a pre-existing group in the Contoso Active Directory. When users are added to the AD group, they're immediately granted privileges.

kind: Role
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: sre-user-full-access
  namespace: sre
rules:
- apiGroups: ["", "extensions", "apps"]
  resources: ["*"]
  verbs: ["*"]
- apiGroups: ["batch"]
  resources:
  - jobs
  - cronjobs
  verbs: ["*"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: ad-user-cluster-admin
  namespace: sre
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: sre-user-full-access
subjects:
  - apiGroup: rbac.authorization.k8s.io
    kind: Group
    name: "microsoft:activedirectory:CONTOSO\SREGroup" 

Before you apply the YAML file, the group and user names should always be converted to SIDs using the command:

kubectl-adsso nametosid <rbac.yml>

Similarly, in order to update an existing RBAC, you can convert the SID to a user-friendly group name before making changes. To convert the SID, use the command:

kubectl-adsso sidtoname <rbac.yml>

Change the AD account password associated with the API server account

When the password is changed for the API server account, you must uninstall the AD authentication add-on and reinstall it using the updated current and previous keytabs.

Every time you change the password, you must rename the current keytab (current.keytab) to previous.keytab. Then, make sure you name the new password current.keytab.

Important

The files must be named current.keytab and previous.keytab, respectively. The existing role bindings are not affected by this change.

Uninstall and reinstall AD authentication

You may want to reinstall AD SSO when the account for the API server is changed, when the password is updated, or to troubleshoot a failure.

To uninstall AD authentication, open PowerShell as an administrator and run the following command:

Uninstall-AksHciAdAuth -name mynewcluster1

To reinstall AD authentication, open PowerShell as an administrator and run the following command:

Install-AksHciAdAuth -name mynewcluster1 -keytab <.\current.keytab> -previousKeytab <.\previous.keytab> -SPN <service/principal@CONTOSO.COM> -adminUser CONTOSO\Bob

Note

To avoid downtime if the clients have cached tickets, the -previousKeytab parameter is required only when you change the password.

Create the API server AD account and the keytab file

Two steps are involved in creating the AD account and keytab file. First, create a new AD account/user for the API server with the service principal name (SPN), and, second, create a keytab file for the AD account.

Step 1: Create a new AD account or user for the API server

Use the New-ADUser PowerShell command to create a new AD account/user with the SPN. Here's an example:

New-ADUser -Name apiserver -ServicePrincipalNames k8s/apiserver -AccountPassword (ConvertTo-SecureString "password" -AsPlainText -Force) -KerberosEncryptionType AES128 -Enabled 1

Step 2: Create the keytab file for the AD account

To create the keytab file, you use the ktpass Windows command.

Here's an example using ktpass:

ktpass /out current.keytab /princ k8s/apiserver@CONTOSO.COM /mapuser contoso\apiserver_acct /crypto all /pass p@$$w0rd /ptype KRB5_NT_PRINCIPAL

Note

If you see the error DsCrackNames returned 0x2 in the name entry, ensure that the parameter for /mapuser is in form mapuser DOMAIN\user, where DOMAIN is the output of echo %userdomain%.

Determine the user or group security identifier

Use one of the following two options to find the SID for your account or other accounts:

  • To find the SID associated with your account, from a command prompt of your home directory, type the following:

    whoami /user
    
  • To find the SID associated with another account, open PowerShell as an administrator and run the following:

    (New-Object System.Security.Principal.NTAccount(<CONTOSO\Bob>)).Translate([System.Security.Principal.SecurityIdentifier]).value
    

Troubleshooting certificates

The webhook and the API server use certificates to mutually validate the TLS connection. This certificate expires in 500 days. To verify that the certificate has expired, view the logs from an ad-auth-webhook container:

kubectl logs ad-auth-webhook-xxx

If you see certificate validation errors, complete the steps to uninstall and reinstall the webhook and get new certificates.

Best practices and cleanup

  • Use a unique account for each cluster.
  • Don't reuse the password for the API server account across clusters.
  • Delete the local copy of the keytab file as soon as you create the cluster and verify that the SSO credentials work.
  • Delete the Active Directory user that was created for the API server. For more information, see Remove-ADUser.

Next steps

In this how-to guide, you learned how to configure AD Authentication to securely connect to the API server with SSO credentials. Next, you can: