All object-oriented programming languages have functions. Functions are used to define a set of procedures that you don’t want to repeat in your template. For example, if you want to write a program to find the factorial of a number and if there are multiple instances throughout the program where you need to find the factorial, instead of writing the code multiple times, you can write a function to find the factorial. Whenever you need to find the factorial of a number, the factorial function will be called, and the number will be passed to the function. With the help of code defined inside the function, it will be able to return the factorial of the number. In the ARM template, functions serve the same purpose.
The following is an example of a function created in an ARM template that can be used to generate unique names for resources that required a unique naming convention. The function will accept a parameter that will be provided by the user and then concatenate that with a string that you defined inside the function. The output of the function will be a unique name that can be used for our resource.
“functions”:[
{
“namespace”: ”azuretales”,
“members”: {
“nameGenerator”: {
“parameters”: [
{
“name”: ”userInput”,
“type”: ”string”
}
],
“output”: {
“value”: ”[concat(toLower(parameters(‘userInput’)),’ax04b-m4′)]”,
“type”: ”string”
}
}
}
}
],
Here the value from the end user is passed to the function via the userInput parameter, and that is converted to a lowercase and then concatenated with the string ax04b-m4 to generate a unique name. Here you use namespace to distinguish this function from other functions in the template.
Variables (variables)
This is yet another concept that you see in all programming and scripting languages. Variables are used to hard-code certain values to keywords so that they can be reused throughout the template. Later, if you need to change the value of an item, you don’t have to change all occurrences; instead, you can update the variable. Once you update the variables, all references will be updated with the new value.
The following is an example of a few variables that are used to describe the name of the virtual network and subnet:
“variables”: {
“vnet”: “vnet-01”,
“vnet-address”: “10.0.0.0/16”,
“subnet-1”: “workload”,
“subnet-1-cidr”: “10.0.0.0/24”
},
As you can see, you are storing certain values that will be used in our template using variables. When you explain the resources section, you will understand how these variables are referenced.