Looping through complex JSON variables in ARM templates - azure

Question

In my ARM template I have a variable called "subnets" which can be of 3 types.
If it is of typeA then I want 4 subnets of the given names and addresses; if it's typeB then 2 subnets, and so on.
"variables": {
"subnets" : {
"typeA" : {
"network" : "3.0/24",
"directory" : "5.0/24",
"documents" : "8.0/24",
"security" : "10.0/24",
},
"typeB" : {
"directory" : "10.0/24",
"database" : "11.0/24",
},
"dmz" : {
"directory" : "12.0/24",
"database" : "15.0/24", }
}
}
In the ARM template I have a parameter which tells me what type to use. So I have a segment like the below which uses a condition to match on the subnetType being typeA and creates a virtual network accordingly.
{
"type": "Microsoft.Network/virtualNetworks",
"condition" : "[contains(parameters('subnetType'), 'typeA')]",
"apiVersion": "2018-10-01",
...
"copy" : [ {
"name" : "subnets",
"count" : "[length(array(variables('subnets').typeA))]",
"input": {
"name": "...",
"properties": {
"addressPrefix": "..."
}
}
} ]
}
}
As you can see above, I have a copy block within this VirtualNetwork resource, and I want to create the various subnets for the typeA network. I figure I could convert subnets.typeA to an array and get the length of it to loop over (that's the idea, I don't know if it actually works) but I am not clear how to extract the subnet name and addressprefix from my variable above.

Answer 1

so there are 2 issues here:
no way to loop object keys in arm templates
use of different resources in the template to create subnets
there is no way to work around the first limitation that I know of, whereas the second limitation is mostly due to you trying to work around the first one. I'd go for a completely different approach:
"networks": [
{
"name": "typeA",
"subnets": [
{
"name": "network",
"addressSpace": "3.0/24"
},
{
"name": "directory",
"addressSpace": "5.0/24"
},
{
"name": "documents",
"addressSpace": "8.0/24"
},
{
"name": "security",
"addressSpace": "10.0/24"
}
]
},
{
// second virtual network
},
{
// x virtual network
}
]
the main downside here - you'd have to have a nested deployment, because you cannot actually iterate array inside array, so you'd have to feed each object inside array into a deployment that would create a virtual network that can contain various subnets.
You can consult this link for an example of this exact approach or the official Azure Building Blocks thingie way of doing this (which is quite similar in the approach, but the implementation is different).
You could, get away with different resources instead of iterations, but that means you are less flexible and each time you make a change to the input everything breaks or just doesnt work like you think it would (your way of doing this would fall apart if dmz doesnt exist in that variable, you'll get a compilation error, similarly if you add another key to the object, say applicationgateway it will work, but that virtual network won't get created)