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CustomScript Extension

Allow the owner of the Azure Virtual Machines to run customized scripts in the VM.

⚠️ New Version Notice ⚠️

A new version of Custom Script Extension is available at https://github.com/Azure/custom-script-extension-linux. The new v2.0 version offers better reliability and wider Linux distro support.

Please consider switching your new deployments to use the new version (Microsoft.Azure.Extensions.CustomScript) instead. The new version is intended to be a drop-in replacement. Therefore, the migration is as easy as changing the name and version, you do not need to change your extension configuration.


This user guide is for Microsoft.OSTCExtensions.CustomScript extension.

You can read the User Guide below.

CustomScript Extension can:

  • If provided, download the customized scripts from Azure Storage or external public storage (e.g. Github)
  • Run the entrypoint script
  • Support inline command
  • Convert Windows style newline in Shell and Python scripts automatically
  • Remove BOM in Shell and Python scripts automatically
  • Protect sensitive data in commandToExecute

Note: The timeout for script download is 200 seconds. There is no timeout period for script execution.

User Guide

1. Configuration schema

1.1. Public configuration

Schema for the public configuration file looks like this:

  • fileUris: (optional, string array) the uri list of the scripts
  • commandToExecute: (required, string) the entrypoint script to execute
  • enableInternalDNSCheck: (optional, bool) default is True, set to False to disable DNS check.
{
  "fileUris": ["<url>"],
  "commandToExecute": "<command-to-execute>"
}

1.2. Protected configuration

Schema for the protected configuration file looks like this:

  • commandToExecute: (optional, string) the entrypoint script to execute
  • storageAccountName: (optional, string) the name of storage account
  • storageAccountKey: (optional, string) the access key of storage account
{
  "commandToExecute": "<command-to-execute>",
  "storageAccountName": "<storage-account-name>",
  "storageAccountKey": "<storage-account-key>"
}

NOTE:

  1. The storage account here is to store the scripts in fileUris. If the scripts are stored in the private Azure Storage, you should provide storageAccountName and storageAccountKey. You can get these two values from Azure Portal. Currently only general purpose storage accounts are supported. We intend to add support for the new Azure Cool Blob Storage in the near future. See #161
  2. commandToExecute in protected settings can protect your sensitive data. But commandToExecute should not be specified both in public and protected configurations.

2. Deploying the Extension to a VM

You can deploy it using Azure CLI, Azure Powershell and ARM template.

NOTE:

Creating VM in Azure has two deployment model: Classic and Resource Manager. In different models, the deploy commands have different syntaxes. Please select the right one in section 2.1 and 2.2 below.

2.1. Using Azure CLI

Before deploying CustomScript Extension, you should configure your public.json and protected.json (in section 1.1 and 1.2 above).

2.1.1 Classic

The Classic mode is also called Azure Service Management mode. You can change to it by running:

$ azure config mode asm

You can deploy CustomScript Extension by running:

$ azure vm extension set <vm-name> \
CustomScriptForLinux Microsoft.OSTCExtensions <version> \
--public-config-path public.json  \
--private-config-path protected.json

In the command above, you can change version with '*' to use latest version available, or '1.*' to get newest version that does not introduce breaking schema changes. To learn the latest version available, run:

$ azure vm extension list

You can also omit --private-config-path if you do not want to configure those settings.

2.1.2 Resource Manager

You can change to Azure Resource Manager mode by running:

$ azure config mode arm

You can deploy CustomScript Extension by running:

$ azure vm extension set <resource-group> <vm-name> \
CustomScriptForLinux Microsoft.OSTCExtensions <version> \
--public-config-path public.json  \
--private-config-path protected.json

NOTE: In ARM mode, azure vm extension list is not available for now.

2.2. Using Azure Powershell

2.2.1 Classic

You can login to your Azure account (Azure Service Management mode) by running:

Add-AzureAccount

You can deploy CustomScript Extension by running:

$VmName = '<vm-name>'
$vm = Get-AzureVM -ServiceName $VmName -Name $VmName

$ExtensionName = 'CustomScriptForLinux'
$Publisher = 'Microsoft.OSTCExtensions'
$Version = '<version>'

$PublicConf = '{
    "fileUris": ["<url>"],
    "commandToExecute": "<command>"
}'
$PrivateConf = '{
    "storageAccountName": "<storage-account-name>",
    "storageAccountKey": "<storage-account-key>"
}'

Set-AzureVMExtension -ExtensionName $ExtensionName -VM $vm `
  -Publisher $Publisher -Version $Version `
  -PrivateConfiguration $PrivateConf -PublicConfiguration $PublicConf |
  Update-AzureVM

2.2.2 Resource Manager

You can login to your Azure account (Azure Resource Manager mode) by running:

Login-AzureRmAccount

Click HERE to learn more about how to use Azure Powershell with Azure Resource Manager.

You can deploy CustomScript Extension by running:

$RGName = '<resource-group-name>'
$VmName = '<vm-name>'
$Location = '<location>'

$ExtensionName = 'CustomScriptForLinux'
$Publisher = 'Microsoft.OSTCExtensions'
$Version = '<version>'

$PublicConf = '{
    "fileUris": ["<url>"],
    "commandToExecute": "<command>"
}'
$PrivateConf = '{
    "storageAccountName": "<storage-account-name>",
    "storageAccountKey": "<storage-account-key>"
}'

Set-AzureRmVMExtension -ResourceGroupName $RGName -VMName $VmName -Location $Location `
  -Name $ExtensionName -Publisher $Publisher `
  -ExtensionType $ExtensionName -TypeHandlerVersion $Version `
  -Settingstring $PublicConf -ProtectedSettingString $PrivateConf

2.3. Using ARM Template

{
  "type": "Microsoft.Compute/virtualMachines/extensions",
  "name": "<extension-deployment-name>",
  "apiVersion": "<api-version>",
  "location": "<location>",
  "dependsOn": [
    "[concat('Microsoft.Compute/virtualMachines/', <vm-name>)]"
  ],
  "properties": {
    "publisher": "Microsoft.OSTCExtensions",
    "type": "CustomScriptForLinux",
    "typeHandlerVersion": "1.5",
    "autoUpgradeMinorVersion": true,
    "settings": {
      "fileUris": [
        "<url>"
      ],
      "commandToExecute": "<command>"
    },
    "protectedSettings": {
      "storageAccountName": "<storage-account-name>",
      "storageAccountKey": "<storage-account-key>"
    }
  }
}

There are two sample templates in Azure/azure-quickstart-templates.

For more details about ARM template, please visit Authoring Azure Resource Manager templates.

3. Scenarios

3.1 Run scripts stored in Azure Storage

  • Public configuration

    {
      "fileUris": ["http://MyAccount.blob.core.windows.net/vhds/MyShellScript.sh"],
      "commandToExecute": " sh MyShellScript.sh"
    }
  • Protected configuration

    {
      "storageAccountName": "MyAccount",
      "storageAccountKey": "Mykey"
    }

3.2 Run scripts stored in GitHub

  • Public configuration

    {
      "fileUris": ["https://github.com/MyProject/Archive/MyPythonScript.py"],
      "commandToExecute": "python MyPythonScript.py"
    }

No need to provide protected settings.

3.3 Run inline scripts

  • Public configuration

    "commandToExecute": "echo Hello"
    "commandToExecute": "python -c \"print 1.4\""

3.4 Run scripts with unchanged configurations

Running scripts with the exactly same configurations is unaccepted in current design. If you need to run scripts repeatly, you can add a timestamp.

  • Public configuration

    {
      "fileUris": ["<url>"],
      "commandToExecute": "<command>",
      "timestamp": 123456789
    }

3.5 Run scripts with sensitive data

  • Public configuration

    {
      "fileUris": ["https://github.com/MyProject/Archive/MyPythonScript.py"]
    }
  • Protected configuration

    {
      "commandToExecute": "python MyPythonScript.py <my-password>"
    }

Supported Linux Distributions

  • CentOS 6.5 and higher
  • Debian 8 and higher
    • Debian 8.7 does not ship with Python2 in the latest images, which breaks CustomScriptForLinux.
  • FreeBSD
  • OpenSUSE 13.1 and higher
  • Oracle Linux 6.4 and higher
  • SUSE Linux Enterprise Server 11 SP3 and higher
  • Ubuntu 12.04 and higher

Debug

  • The status of the extension is reported back to Azure so that user can see the status on Azure Portal
  • All the execution output and error of the scripts are logged into the download directory of the scripts /var/lib/waagent/<extension-name-and-version>/download/<seq>/, and the tail of the output is logged into the log directory specified in HandlerEnvironment.json and reported back to Azure
  • The operation log of the extension is /var/log/azure/<extension-name>/<version>/extension.log file.
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