A quick look at azure/kubelogin

I have talked about and demonstrated the use of kubelogin in previous posts and videos. Because I often get questions about logging on to Azure Kubernetes Services (AKS) integrated with Azure AD (AAD) in a non-interactive fashion, I decided to write this separate post about it.

What is kubelogin?

Kubelogin is a client-go credential plugin that implements Azure AD authentication. Kubernetes and its CLI, kubectl, are written in Go and client-go is a package or library that allows you to talk to Kubernetes from the Go language. Client-go supports credentials plugins to integrate with authentication protocols that are not supported by default by kubectl. Do not confuse azure/kubelogin with int128/kubelogin. The latter is a generic credential plugin that supports OpenID Connect in general, while the former was specifically created for Azure.

Why use it?

When you integrate an AKS cluster with Azure AD, you can grant users and groups in Azure AD, access rights to your cluster. You do that via Kubernetes RBAC or Azure RBAC for Kubernetes. Once you have assigned the necessary access rights to the user or group, a user can login by first obtaining credentials with the Azure CLI:

az aks get-credentials -n CLUSTERNAME -g RESOURCEGROUP

After running the above command, the user will not be asked to authenticate yet. However, when a command such as kubectl get nodes is run, the user will need to authenticate to Azure AD by opening a browser and entering a code:

Prompted to enter a code

When the code is entered, and the user has the necessary role to run the command, the output will appear.

This is great when you are working interactively on the command line but not so great in a pipeline. Often, engineers circumvent this by using:

az aks get-credentials -n CLUSTERNAME -g RESOURCEGROUP --admin

The use of –admin switches to client certificate authentication and gives you full control of the cluster. In general, this is not recommended. It is worth noting that, at the time of this writing, there is also a preview feature that can disable the use of local accounts.

What to do in a pipeline?

In a pipeline, the easiest way to login with an Azure AD account is as follows:

  • Use the Azure CLI and logon with an account that has the required role on the Kubernetes cluster
  • Use az aks get-credentials to obtain cluster credentials and DO NOT use –admin; this creates a kube config file on the CI/CD agent (e.g. GitHub runner, Azure DevOps agent, etc…)
  • Download kubelogin if required (mostly, that will be needed)
  • Use kubelogin to update the kube config file with the token of the Azure CLI user; this is one of the options and has been added in March of 2021

Check out the following sample Azure DevOps pipeline below:

trigger: none

pool:
  vmImage: ubuntu-latest

steps:
- task: KubectlInstaller@0
  inputs:
    kubectlVersion: 'latest'

- task: AzureCLI@2
  inputs:
    azureSubscription: 'NAME OF AZURE DEVOPS SERVICE CONNECTION'
    scriptType: 'bash'
    scriptLocation: 'inlineScript'
    inlineScript: |
      az aks get-credentials -n CLUSTERNAME -g CLUSTERRESOURCEGROUP

      # get kubelogin
      wget https://github.com/Azure/kubelogin/releases/download/v0.0.9/kubelogin-linux-amd64.zip
      unzip kubelogin-linux-amd64.zip
      sudo mv bin/linux_amd64/kubelogin /usr/bin
      kubelogin convert-kubeconfig -l azurecli

      kubectl get nodes

In Azure DevOps, you can specify a name of a service connection in the azureSubscription parameter of the AzureCLI@2 task. The account used by the service connection needs access rights to the Kubernetes cluster.

The command kubelogin convert-kubeconfig -l azurecli modifies the kube config obtained with az aks get-credentials with a token for the account used by the Azure CLI. To use the Azure CLI credential, you have to use managed AAD integration.

Although the above is for Azure DevOps, the process is similar for other CI/CD systems such as GitHub workflows. In GitHub, you can use the azure/CLI action, which requires an azure/login action first. The azure/login action uses a service principal to connect. That service principal needs access rights to the Kubernetes cluster.

Note that there are many other ways to obtain the token. You are not restricted to use the Azure CLI credentials. You can also use your own service principal or a managed service identity (MSI). Check the README of azure/kubelogin for more info.

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