ARM Template Tip: Names

Naming resources in ARM templates can be quite lengthy. This is an example of naming a network interface:

"name": "[concat(parameters('vmNamePrefix'), '-', padLeft(copyIndex(1), 2, '0'), variables('nicPostfix'), '-', padLeft(copyIndex(1), 2, '0'))]",

And we have to reference this at a later point for the virtual machine resource. If we then change the name, we will have to remember to change this reference also.

What we can do is to define the name in the variables section like this:

    "nic": {
      "name": "[concat(parameters('vmNamePrefix'), '-', padLeft('{0}', 4, '0'), variables('nicPostfix'), '-', padLeft('{0}', 4, '0'))]"
    }

(I like to group variables). And then reference this variable in the resource like:

"name": "[replace(variables('nic').name, '{0}', string(copyIndex(1)))]",

What I have done is to make {0} a placeholder and then replace it with the result from copyIndex(). We now have a central location to change the name if needed with no need to update any resources.

Would be cool if we had a template function for formatting:

"name": "[format(variables('nic').name, copyIndex(1), '-nic')]"

It would take the string as input and then a variable number of additional arguments. Ex.

"nic": {
   "name": "concat(parameters('vmNamePrefix'), '0{0}', '{1}')]"
}

would become({0} is replaced with the result from copyIndex(1) and {1} replaced with -nic):

"VM01-nic"

And it could be made more advanced, perhaps leaning on the good ol' sprintf.