Connect to Azure Kubernetes Service (AKS) cluster nodes for maintenance or troubleshooting

Throughout the lifecycle of your Azure Kubernetes Service (AKS) cluster, you eventually need to directly access an AKS node. This access could be for maintenance, log collection, or troubleshooting operations.

You access a node through authentication, which methods vary depending on your Node OS and method of connection. You securely authenticate against AKS Linux and Windows nodes through two options discussed in this article. One requires that you have Kubernetes API access, and the other is through the AKS ARM API, which provides direct private IP information. For security reasons, AKS nodes aren't exposed to the internet. Instead, to connect directly to any AKS nodes, you need to use either kubectl debug or the host's private IP address.

Access nodes using the Kubernetes API

This method requires usage of kubectl debug command.

Before you begin

This guide shows you how to create a connection to an AKS node and update the SSH key of your AKS cluster. To follow along the steps, you need to use Azure CLI that supports version 2.0.64 or later. Run az --version to check the version. If you need to install or upgrade, see Install Azure CLI.

Complete these steps if you don't have an SSH key. Create an SSH key depending on your Node OS Image, for macOS and Linux, or Windows. Make sure you save the key pair in the OpenSSH format, avoid unsupported formats such as .ppk. Next, refer to Manage SSH configuration to add the key to your cluster.

Linux and macOS

Linux and macOS users can SSH to access their node using kubectl debug or their private IP Address. Windows users should skip to the Windows Server Proxy section for a workaround to SSH via proxy.

SSH using kubectl debug

To create an interactive shell connection, use the kubectl debug command to run a privileged container on your node.

  1. To list your nodes, use the kubectl get nodes command:

    kubectl get nodes -o wide
    

    Sample output:

    NAME                                STATUS   ROLES   AGE    VERSION   INTERNAL-IP   EXTERNAL-IP   OS-IMAGE
    aks-nodepool1-37663765-vmss000000   Ready    agent   166m   v1.25.6   10.224.0.33   <none>        Ubuntu 22.04.2 LTS
    aks-nodepool1-37663765-vmss000001   Ready    agent   166m   v1.25.6   10.224.0.4    <none>        Ubuntu 22.04.2 LTS
    aksnpwin000000                      Ready    agent   160m   v1.25.6   10.224.0.62   <none>        Windows Server 2022 Datacenter
    
  2. Use the kubectl debug command to start a privileged container on your node and connect to it.

    kubectl debug node/aks-nodepool1-37663765-vmss000000 -it --image=mcr.microsoft.com/cbl-mariner/busybox:2.0
    

    Sample output:

    Creating debugging pod node-debugger-aks-nodepool1-37663765-vmss000000-bkmmx with container debugger on node aks-nodepool1-37663765-vmss000000.
    If you don't see a command prompt, try pressing enter.
    root@aks-nodepool1-37663765-vmss000000:/#
    

    You now have access to the node through a privileged container as a debugging pod.

    Note

    You can interact with the node session by running chroot /host from the privileged container.

Exit kubectl debug mode

When you're done with your node, enter the exit command to end the interactive shell session. After the interactive container session closes, delete the debugging pod used with kubectl delete pod.

kubectl delete pod node-debugger-aks-nodepool1-37663765-vmss000000-bkmmx

Windows Server proxy connection for SSH

Follow these steps as a workaround to connect with SSH on a Windows Server node.

Create a proxy server

At this time, you can't connect to a Windows Server node directly by using kubectl debug. Instead, you need to first connect to another node in the cluster with kubectl, then connect to the Windows Server node from that node using SSH.

To connect to another node in the cluster, use the kubectl debug command. For more information, follow the above steps in the kubectl section. Create an SSH connection to the Windows Server node from another node using the SSH keys provided when you created the AKS cluster and the internal IP address of the Windows Server node.

Important

The following steps for creating the SSH connection to the Windows Server node from another node can only be used if you created your AKS cluster using the Azure CLI with the --generate-ssh-keys parameter. If you want to use your own SSH keys instead, you can use the az aks update to manage SSH keys on an existing AKS cluster. For more information, see manage SSH node access.

Note

If your Linux proxy node is down or unresponsive, use the Azure Bastion method to connect instead.

  1. Use the kubectl debug command to start a privileged container on your proxy (Linux) node and connect to it.

    kubectl debug node/aks-nodepool1-37663765-vmss000000 -it --image=mcr.microsoft.com/cbl-mariner/busybox:2.0
    

    Sample output:

    Creating debugging pod node-debugger-aks-nodepool1-37663765-vmss000000-bkmmx with container debugger on node aks-nodepool1-37663765-vmss000000.
    If you don't see a command prompt, try pressing enter.
    root@aks-nodepool1-37663765-vmss000000:/#
    
  2. Open a new terminal window and use the kubectl get pods command to get the name of the pod started by kubectl debug.

    kubectl get pods
    

    Sample output:

    NAME                                                    READY   STATUS    RESTARTS   AGE
    node-debugger-aks-nodepool1-37663765-vmss000000-bkmmx   1/1     Running   0          21s
    

    In the sample output, node-debugger-aks-nodepool1-37663765-vmss000000-bkmmx is the name of the pod started by kubectl debug.

  3. Use the kubectl port-forward command to open a connection to the deployed pod:

    kubectl port-forward node-debugger-aks-nodepool1-37663765-vmss000000-bkmmx 2022:22
    

    Sample output:

    Forwarding from 127.0.0.1:2022 -> 22
    Forwarding from [::1]:2022 -> 22
    

    The previous example begins forwarding network traffic from port 2022 on your development computer to port 22 on the deployed pod. When using kubectl port-forward to open a connection and forward network traffic, the connection remains open until you stop the kubectl port-forward command.

  4. Open a new terminal and run the command kubectl get nodes to show the internal IP address of the Windows Server node:

    kubectl get no -o custom-columns=NAME:metadata.name,'INTERNAL_IP:status.addresses[?(@.type == \"InternalIP\")].address'
    

    Sample output:

    NAME                                INTERNAL_IP
    aks-nodepool1-19409214-vmss000003   10.224.0.8
    

    In the previous example, 10.224.0.62 is the internal IP address of the Windows Server node.

  5. Create an SSH connection to the Windows Server node using the internal IP address, and connect to port 22 through port 2022 on your development computer. The default username for AKS nodes is azureuser. Accept the prompt to continue with the connection. You're then provided with the bash prompt of your Windows Server node:

    ssh -o 'ProxyCommand ssh -p 2022 -W %h:%p azureuser@127.0.0.1' azureuser@10.224.0.62
    

    Sample output:

    The authenticity of host '10.224.0.62 (10.224.0.62)' can't be established.
    ECDSA key fingerprint is SHA256:1234567890abcdefghijklmnopqrstuvwxyzABCDEFG.
    Are you sure you want to continue connecting (yes/no)? yes
    

    Note

    If you prefer to use password authentication, include the parameter -o PreferredAuthentications=password. For example:

     ssh -o 'ProxyCommand ssh -p 2022 -W %h:%p azureuser@127.0.0.1' -o PreferredAuthentications=password azureuser@10.224.0.62
    

Use Host Process Container to access Windows node

  1. Create hostprocess.yaml with the following content and replacing AKSWINDOWSNODENAME with the AKS Windows node name.

    apiVersion: v1
    kind: Pod
    metadata:
      labels:
        pod: hpc
      name: hpc
    spec:
      securityContext:
        windowsOptions:
          hostProcess: true
          runAsUserName: "NT AUTHORITY\\SYSTEM"
      hostNetwork: true
      containers:
        - name: hpc
          image: mcr.microsoft.com/windows/servercore:ltsc2022 # Use servercore:1809 for WS2019
          command:
            - powershell.exe
            - -Command
            - "Start-Sleep 2147483"
          imagePullPolicy: IfNotPresent
      nodeSelector:
        kubernetes.io/os: windows
        kubernetes.io/hostname: AKSWINDOWSNODENAME
      tolerations:
        - effect: NoSchedule
          key: node.kubernetes.io/unschedulable
          operator: Exists
        - effect: NoSchedule
          key: node.kubernetes.io/network-unavailable
          operator: Exists
        - effect: NoExecute
          key: node.kubernetes.io/unreachable
          operator: Exists
    
  2. Run kubectl apply -f hostprocess.yaml to deploy the Windows host process container (HPC) in the specified Windows node.

  3. Use kubectl exec -it [HPC-POD-NAME] -- powershell.

  4. You can run any PowerShell commands inside the HPC container to access the Windows node.

Note

You need to switch the root folder to C:\ inside the HPC container to access the files in the Windows node.

SSH using Azure Bastion for Windows

If your Linux proxy node isn't reachable, using Azure Bastion as a proxy is an alternative. This method requires that you set up an Azure Bastion host for the virtual network in which the cluster resides. See Connect with Azure Bastion for more details.

SSH using private IPs from the AKS API (preview)

If you don't have access to the Kubernetes API, you can get access to properties such as Node IP and Node Name through the AKS agent pool API (preview), (available on preview versions 07-02-2023 or above) to connect to AKS nodes.

Important

AKS preview features are available on a self-service, opt-in basis. Previews are provided "as is" and "as available," and they're excluded from the service-level agreements and limited warranty. AKS previews are partially covered by customer support on a best-effort basis. As such, these features aren't meant for production use. For more information, see the following support articles:

Create an interactive shell connection to a node using the IP address

For convenience, AKS nodes are exposed on the cluster's virtual network through private IP addresses. However, you need to be in the cluster's virtual network to SSH into the node. If you don't already have an environment configured, you can use Azure Bastion to establish a proxy from which you can SSH to cluster nodes. Make sure the Azure Bastion is deployed in the same virtual network as the cluster.

  1. Obtain private IPs using the az aks machine list command, targeting all the VMs in a specific node pool with the --nodepool-name flag.

        az aks machine list --resource-group myResourceGroup  --cluster-name myAKSCluster --nodepool-name nodepool1 -o table
    

    The following example output shows the internal IP addresses of all the nodes in the node pool:

      Name                               Ip         Family    
    ---------------------------------  -----------  ----------- 
    aks-nodepool1-33555069-vmss000000  10.224.0.5   IPv4
    aks-nodepool1-33555069-vmss000001  10.224.0.6   IPv4
    aks-nodepool1-33555069-vmss000002  10.224.0.4   IPv4            
    

    To target a specific node inside the node pool, use the --machine-name flag:

        az aks machine show --cluster-name myAKScluster --nodepool-name nodepool1 -g myResourceGroup --machine-name aks-nodepool1-33555069-vmss000000 -o table
    

    The following example output shows the internal IP address of all the specified node:

      Name                               Ip         Family    
    ---------------------------------  -----------  ----------- 
    aks-nodepool1-33555069-vmss000000  10.224.0.5   IPv4
       ```
    
    
  2. SSH to the node using the private IP address you obtained in the previous step. This step is applicable for Linux machines only. For Windows machines, see Connect with Azure Bastion.

    ssh -i /path/to/private_key.pem azureuser@10.224.0.33
    

Next steps

If you need more troubleshooting data, you can view the kubelet logs or view the Kubernetes control plane logs.

To learn about managing your SSH keys, see Manage SSH configuration.