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Key Vault virtual machine extension for Linux

  • Άρθρο

The Key Vault VM extension provides automatic refresh of certificates stored in an Azure key vault. Specifically, the extension monitors a list of observed certificates stored in key vaults. The extension retrieves and installs the corresponding certificates after detecting a change. This document details the supported platforms, configurations, and deployment options for the Key Vault VM extension for Linux.

Operating system

The Key Vault VM extension supports these Linux distributions:

Note

The Key Vault VM Extension downloads the certificates in the default location or to the location provided by "certStoreLocation" property in the VM Extension settings (version 1/2), or individual certificate settings (version 3). The Key Vault VM Extension updates the folder permission to 700 (drwx------) allowing read, write and execute permission to the owner of the folder only

Supported certificate content types

  • PKCS #12
  • PEM

Updates in Version 3.0+

Version 3.0+ of the Key Vault VM extension for Linux adds support for the following features:

  • Add ACL permissions for downloaded certificates to provide read access for users and groups
  • Certificate installation location configuration
  • Custom symbolic name support
  • VM extension logging integration support through Fluentd

Prerequisites

  • Key Vault instance with certificate. See Create a Key Vault

  • Assigned managed identity on VM/VMSS

  • The Key Vault Secrets User role at the Key Vault scope level for VMs and Azure Virtual Machine Scale Sets managed identity. This role retrieves a secret's portion of a certificate. For more information, see the following articles:

  • VMSS should have the following identity setting: "identity": { "type": "UserAssigned", "userAssignedIdentities": { "[parameters('userAssignedIdentityResourceId')]": {} } }

  • AKV extension should have this setting: "authenticationSettings": { "msiEndpoint": "[parameters('userAssignedIdentityEndpoint')]", "msiClientId": "[reference(parameters('userAssignedIdentityResourceId'), variables('msiApiVersion')).clientId]" }

Key Vault VM extension version

  • Users can choose to upgrade their existing Key Vault VM extension version to newer version.

  • If you prefer to upgrade to newer version, you would need to delete previous version first, then install newer version.

  az vm extension delete --name KeyVaultForLinux --resource-group ${resourceGroup} --vm-name ${vmName}
  az vm extension set -n "KeyVaultForLinux" --publisher Microsoft.Azure.KeyVault --resource-group "${resourceGroup}" --vm-name "${vmName}" –settings .\akvvm.json –version 3.0

The flag --version 3.0 is optional because the latest version is installed by default.

  • If the VM has certificates downloaded by previous version, deleting VM extension doesn't delete the downloaded certificates. After installing newer version, the existing certificates aren't modified. You would need to delete the certificate files or roll-over the certificate to get the PEM file with full-chain on the VM.

Extension schema

The following JSON shows the schema for the Key Vault VM extension. The extension doesn't require protected settings - all its settings are considered information without security impact. The extension requires a list of monitored secrets, polling frequency, and the destination certificate store. Specifically:

    {
      "type": "Microsoft.Compute/virtualMachines/extensions",
      "name": "KVVMExtensionForLinux",
      "apiVersion": "2022-11-01",
      "location": "<location>",
      "dependsOn": [
          "[concat('Microsoft.Compute/virtualMachines/', <vmName>)]"
      ],
      "properties": {
      "publisher": "Microsoft.Azure.KeyVault",
      "type": "KeyVaultForLinux",
      "typeHandlerVersion": "3.0",
      "autoUpgradeMinorVersion": true,
      "enableAutomaticUpgrade": true,
      "settings": {
      "loggingSettings": <Optional logging settings, e.g.:
        {
              "logger": <Logger engine name. e.g.: "fluentd">,
              "endpoint": <Logger listening endpoint "tcp://localhost:24224">,
              "format": <Logging format. e.g.: "forward">,
              "servicename": <Service name used in logs. e.g.: "akvvm_service">
          }>,
        "secretsManagementSettings": {
          "pollingIntervalInS": <polling interval in seconds, e.g. "3600">,
          "linkOnRenewal": <Not available on Linux e.g.: false>,
          "requireInitialSync": <initial synchronization of certificates e..g: true>,
          "aclEnabled": <Enables ACLs for downloaded certificates, e.g.: true>,
          "observedCertificates": <An array of KeyVault URIs that represent monitored certificates, including certificate store location, ACL permission to certificate private key, and custom symbolic name. e.g.: 
             [
                {
                    "url": <A Key Vault URI to the secret portion of the certificate. e.g.: "https://myvault.vault.azure.net/secrets/mycertificate1">,
                    "certificateStoreLocation": <disk path where certificate is stored, e.g.: "/var/lib/waagent/Microsoft.Azure.KeyVault/app1">,
                    "customSymbolicLinkName": <symbolic name for the certificate. e.g.: "app1Cert1">,
                    "acls": [
                        {
                            "user": "app1",
                            "group": "appGroup1"
                        },
                        {
                            "user": "service1"
                        }
                    ]
                },
                {
                    "url": <Example: "https://myvault.vault.azure.net/secrets/mycertificate2">,
                    "certificateStoreLocation": <disk path where the certificate is stored, e.g.: "/var/lib/waagent/Microsoft.Azure.KeyVault/app2">,
                    "acls": [
                        {
                            "user": "app2",
                        }
                    ]
                }
             ]>
        },
        "authenticationSettings": <Optional msi settings, e.g.:
        {
          "msiEndpoint":  <Required when msiClientId is provided. MSI endpoint e.g. for most Azure VMs: "http://169.254.169.254/metadata/identity">,
          "msiClientId":  <Required when VM has any user assigned identities. MSI identity e.g.: "c7373ae5-91c2-4165-8ab6-7381d6e75619".>
        }>
       }
      }
    }

Note

Your observed certificates URLs should be of the form https://myVaultName.vault.azure.net/secrets/myCertName.

This is because the /secrets path returns the full certificate, including the private key, while the /certificates path doesn't. More information about certificates can be found here: Key Vault Certificates

Important

The 'authenticationSettings' property is required for VMs with any user assigned identities. Even if you want to use a system assigned identity this is still required otherwise the VM extension doesn't know which identity to use. Without this section, a VM with user assigned identities will result in the Key Vault extension failing and being unable to download certificates. Set msiClientId to the identity that will authenticate to Key Vault.

Also required for Azure Arc-enabled VMs. Set msiEndpoint to http://localhost:40342/metadata/identity.

Property values

Name Value / Example Data Type
apiVersion 2022-07-01 date
publisher Microsoft.Azure.KeyVault string
type KeyVaultForLinux string
typeHandlerVersion 3.0 int
pollingIntervalInS 3600 string
certificateStoreName It's ignored on Linux string
linkOnRenewal false boolean
requireInitialSync true boolean
aclEnabled true boolean
certificateStoreLocation /var/lib/waagent/Microsoft.Azure.KeyVault.Store string
observedCertificates [{...}, {...}] string array
observedCertificates/url "https://myvault.vault.azure.net/secrets/mycertificate1" string
observedCertificates/certificateStoreLocation "/var/lib/waagent/Microsoft.Azure.KeyVault/app1" string
observedCertificates/customSymbolicLinkName (optional) "app1Cert1" string
observedCertificates/acls (optional) "{...}, {...}" string array
authenticationSettings (optional) {...} object
authenticationSettings/msiEndpoint http://169.254.169.254/metadata/identity string
authenticationSettings/msiClientId c7373ae5-91c2-4165-8ab6-7381d6e75619 string
loggingSettings (optional) {...} object
loggingSettings/logger "fluentd" string
loggingSettings/endpoint "tcp://localhost:24224" string
loggingSettings/format "forward" string
loggingSettings/servicename "akvvm_service" string

Template deployment

Azure VM extensions can be deployed with Azure Resource Manager templates. Templates are ideal when deploying one or more virtual machines that require post deployment refresh of certificates. The extension can be deployed to individual VMs or virtual machine scale sets. The schema and configuration are common to both template types.

The JSON configuration for a virtual machine extension must be nested inside the virtual machine resource fragment of the template, specifically "resources": [] object for the virtual machine template and for a virtual machine scale set under "virtualMachineProfile":"extensionProfile":{"extensions" :[] object.

Note

The VM extension would require system or user managed identity to be assigned to authenticate to Key vault. See How to authenticate to Key Vault and assign a Key Vault access policy.

   {
      "type": "Microsoft.Compute/virtualMachines/extensions",
      "name": "KeyVaultForLinux",
      "apiVersion": "2022-11-01",
      "location": "<location>",
      "dependsOn": [
          "[concat('Microsoft.Compute/virtualMachines/', <vmName>)]"
      ],
      "properties": {
      "publisher": "Microsoft.Azure.KeyVault",
      "type": "KeyVaultForLinux",
      "typeHandlerVersion": "3.0",
      "autoUpgradeMinorVersion": true,
      "enableAutomaticUpgrade": true,
      "settings": {
          "secretsManagementSettings": {
          "pollingIntervalInS": <polling interval in seconds, e.g. "3600">,
          "requireInitialSync": <initial synchronization of certificates e..g: false>,
          "aclEnabled": <enables/disables acls on defined certificates e.g.: true>,
          "observedCertificates": <An array of KeyVault URIs that represent monitored certificates, including certificate store location and ACL permission to certificate private key. Example:
             [
                {
                    "url": <A Key Vault URI to the secret portion of the certificate. Example: "https://myvault.vault.azure.net/secrets/mycertificate1">,
                    "certificateStoreLocation": <The certificate store location, which currently works locally only. Example: "/var/lib/waagent/Microsoft.Azure.KeyVault.Store">,
                    "acls": <Optional. An array of preferred acls with read access to certificate private keys. Example: 
                    [
                        {
                            "user": "app1",
                            "group": "appGroup1"
                        },
                        {
                            "user": "service1"
                        }
                    ]>
                },
                {
                    "url": <Example: "https://myvault.vault.azure.net/secrets/mycertificate2">,
                    "certificateStoreName": <ignored on linux>,
                    "certificateStoreLocation": <The certificate store location, which currently works locally only. Example: "/var/lib/waagent/Microsoft.Azure.KeyVault.Store">,
                    "acls": <Optional. An array of preferred acls with read access to certificate private keys. Example: 
                    [
                        {
                            "user": "app2"
                        }
                    ]>
                }
               
             ]>   
          },
          "authenticationSettings": {
              "msiEndpoint":  <Required when msiClientId is provided. MSI endpoint e.g. for most Azure VMs: "http://169.254.169.254/metadata/identity">,
              "msiClientId":  <Required when VM has any user assigned identities. MSI identity e.g.: "c7373ae5-91c2-4165-8ab6-7381d6e75619">
          }
        } 
      }
    }

Extension Dependency Ordering

The Key Vault VM extension supports extension ordering if configured. By default the extension reports successful start as soon as polling starts. However, you can configure it to wait until it successfully downloads the complete list of certificates before reporting a successful start. If other extensions depend on installed certificates before they start, then enabling this setting will allow those extensions to declare a dependency on the Key Vault extension. This will prevent those extensions from starting until all certificates they depend on have been installed. The extension will retry the initial download indefinitely and remain in a Transitioning state.

To turn on extension dependency, set the following:

"secretsManagementSettings": {
    "requireInitialSync": true,
    ...
}

Note

Using this feature is not compatible with an ARM template that creates a system assigned identity and updates a Key Vault access policy with that identity. Doing so will result in a deadlock as the vault access policy cannot be updated until all extensions have started. You should instead use a single user assigned MSI identity and pre-ACL your vaults with that identity before deploying.

Azure PowerShell deployment

Warning

PowerShell clients often add \ to " in the settings.json which will cause akvvm_service fails with error: [CertificateManagementConfiguration] Failed to parse the configuration settings with:not an object.

The Azure PowerShell can be used to deploy the Key Vault VM extension to an existing virtual machine or virtual machine scale set.

  • To deploy the extension on a VM:

The Azure Key Vault VM extension can be deployed with Azure PowerShell. Save Key Vault VM extension settings to a JSON file (settings.json).

The following JSON snippets provide example settings for deploying the Key Vault VM extension with PowerShell.

{
   "secretsManagementSettings": {
   "pollingIntervalInS": "3600",
   "linkOnRenewal": true,
   "aclEnabled": true,
   "observedCertificates":
   [
      {
          "url": "https://<examplekv>.vault.azure.net/secrets/mycertificate1",
          "certificateStoreLocation":  "/var/lib/waagent/Microsoft.Azure.KeyVault.Store",
          "acls": 
          [
              {
                  "user": "app1",
                  "group": "appGroup1"
              },
              {
                  "user": "service1"
              }
          ]
      },
      {
          "url": "https://<examplekv>.vault.azure.net/secrets/mycertificate2",
          "certificateStoreLocation": "/var/lib/waagent/Microsoft.Azure.KeyVault.Store",
          "acls": 
          [
              {
                  "user": "app2"
              }
          ]
      }
   ]},
   "authenticationSettings": {
      "msiEndpoint":  "http://169.254.169.254/metadata/identity/oauth2/token",
      "msiClientId":  "xxxxxx-xxxx-xxxx-xxxx-xxxxxxxx"
   }      
}
  • To deploy the extension on a virtual machine:
# Build settings
$settings = (get-content -raw ".\settings.json")
$extName =  "KeyVaultForLinux"
$extPublisher = "Microsoft.Azure.KeyVault"
$extType = "KeyVaultForLinux"
 
# Start the deployment
Set-AzVmExtension -TypeHandlerVersion "3.0" -ResourceGroupName <ResourceGroupName> -Location <Location> -VMName <VMName> -Name $extName -Publisher $extPublisher -Type $extType -SettingString $settings
  • To deploy the extension on a virtual machine scale set:
    # Build settings
    $settings = (get-content -raw ".\settings.json")
    $extName = "KeyVaultForLinux"
    $extPublisher = "Microsoft.Azure.KeyVault"
    $extType = "KeyVaultForLinux"
      
    # Add extension to Virtual Machine Scale Sets
    $vmss = Get-AzVmss -ResourceGroupName <ResourceGroupName> -VMScaleSetName <VmssName>
    Add-AzVmssExtension -VirtualMachineScaleSet $vmss  -Name $extName -Publisher $extPublisher -Type $extType -TypeHandlerVersion "3.0" -Setting $settings
    
    # Start the deployment
    Update-AzVmss -ResourceGroupName <ResourceGroupName> -VMScaleSetName <VmssName> -VirtualMachineScaleSet $vmss

Azure CLI deployment

The Azure CLI can be used to deploy the Key Vault VM extension to an existing virtual machine or virtual machine scale set.

  • To deploy the extension on a VM:

The Azure Key Vault VM extension can be deployed by using the Azure CLI. Save Key Vault VM extension settings to a JSON file (settings.json).

The following JSON snippets provide example settings for deploying the Key Vault VM extension with the Azure CLI.

{
   "secretsManagementSettings": {
   "pollingIntervalInS": "3600",
   "linkOnRenewal": true,
   "aclEnabled": true,
   "observedCertificates":
   [
      {
          "url": "https://<examplekv>.vault.azure.net/secrets/mycertificate1",
          "certificateStoreLocation":  "/var/lib/waagent/Microsoft.Azure.KeyVault.Store",
          "acls": 
          [
              {
                  "user": "app1",
                  "group": "appGroup1"
              },
              {
                  "user": "service1"
              }
          ]
      },
      {
          "url": "https://<examplekv>.vault.azure.net/secrets/mycertificate2",
          "certificateStoreLocation": "/var/lib/waagent/Microsoft.Azure.KeyVault.Store",
          "acls": 
          [
              {
                  "user": "app2"
              }
          ]
      }
   ]},
   "authenticationSettings": {
      "msiEndpoint":  "http://169.254.169.254/metadata/identity/oauth2/token",
      "msiClientId":  "xxxxxx-xxxx-xxxx-xxxx-xxxxxxxx"
   }      
}
  • To deploy the extension on a virtual machine

    # Start the deployment
      az vm extension set -n "KeyVaultForLinux" `
      --publisher Microsoft.Azure.KeyVault `
      -g "<resourcegroup>" `
      --vm-name "<vmName>" `
      --version 3.0 `
      --enable-auto-upgrade true `
      --settings "@settings.json"
  • To deploy the extension on a virtual machine scale set:
    # Start the deployment
    az vmss extension set -n "KeyVaultForLinux" `
    --publisher Microsoft.Azure.KeyVault `
    -g "<resourcegroup>" `
    --vmss-name "<vmssName>" `
    --version 3.0 `
    --enable-auto-upgrade true `
    --settings "@settings.json"

Please be aware of the following restrictions/requirements:

  • Key Vault restrictions:
    • It must exist at the time of the deployment
    • The Key Vault Secrets User role must be assigned to Key Vault for VM identity

Troubleshoot and Support

Data about the state of extension deployments can be retrieved from the Azure portal, and by using the Azure PowerShell. To see the deployment state of extensions for a given VM, run the following command using the Azure PowerShell.

Azure PowerShell

Get-AzVMExtension -VMName <vmName> -ResourceGroupname <resource group name>

Azure CLI

 az vm get-instance-view --resource-group <resource group name> --name  <vmName> --query "instanceView.extensions"

The Azure CLI can run in several shell environments, but with slight format variations. If you have unexpected results with Azure CLI commands, see How to use the Azure CLI successfully.

Logs and configuration

The Key Vault VM extension logs exist locally on the VM and are most informative when it comes to troubleshooting. You can use optional logging section to integrate with logging provider through fluentd

Location Description
/var/log/waagent.log Shows when an update to the extension occurred.
/var/log/azure/Microsoft.Azure.KeyVault.KeyVaultForLinux/* Examine the Key Vault VM Extension service logs to determine the status of the akvvm_service service and certificate download. You can find the download location of PEM files in files with an entry called certificate file name. If certificateStoreLocation is not specified, it will default to /var/lib/waagent/Microsoft.Azure.KeyVault.Store/
/var/lib/waagent/Microsoft.Azure.KeyVault.KeyVaultForLinux-<most recent version>/config/* The configuration and binaries for Key Vault VM Extension service.

Symbolic links or Symlinks are advanced shortcuts. To avoid monitoring the folder and to get the latest certificate automatically, you can use this symlink ([VaultName].[CertificateName]) to get the latest version of certificate on Linux.

Frequently Asked Questions

  • Is there's a limit on the number of observedCertificates you can configure? No, Key Vault VM Extension doesn’t have limit on the number of observedCertificates.

Support

If you need more help at any point in this article, you can contact the Azure experts on the MSDN Azure and Stack Overflow forums. Alternatively, you can file an Azure support incident. Go to the Azure support site and select Get support. For information about using Azure Support, read the Microsoft Azure support FAQ.