Azure ARMory: Including customData without a fuss

Shane R. Spencer

·Nov 5, 2020

Include a plain text cloud-init file using secureString variable types and backticks in your Azure ARM template

Beware! I’m a smidge new to Azure and only recently started fooling around with the template deployment functions. That said… even though it requires quite a shift going from manpages to Azure technical propaganda… it appears ARM templates are fairly straight forward after some initial demystification.

When I went to download my template after using the Azure portal to set up a virtual machine deployment I was a bit dismayed to see that the customData I had included as a cloud-init compatibleuser-data.txt data had somehow evaporated and not made it in to the template.json or the parameters.json files.

Turns out this isn’t a very common scenario. So lets get right to it.

First off your downloaded template.json for a virtual machine will(should) already contain the variable definition for customData under the root parameters key.

{
  "parameters": {
    "customData": {
      "type": "secureString"
    }
  }
}

Under the osProfile key further down the file you will(should) also see the customData placement and code to include the parameter.

{
  "resources": [
    {
      "properties": {
        "osProfile": {
          "customData": "[parameters('customData')]"
        }
      }
    }
  ]
}

Assuming you are using the CLI tools provided for Linux/MacOS and not Powershell you can now run the following to include your customData during deployment by way of the magic shell backticks and the base64 tool set to 0 (disabled) wrapping width.

az deployment group create --resource-group Development --template-file template.json --parameters @parameters.json --parameters customData="`base64 -w 0 cloud-init`"

Enjoy!