Why is the ID for a subnet created using Azure Resource Manager Powershell cmdlets null?

Question

I am trying to provision some network resources in Azure and I am running into a blocker with a step that tries to reference a previously created subnet's Id property.

Here's the command to retrieve the subnet details:

$gwsubnet = Get-AzureRmVirtualNetworkSubnetConfig -Name 'GatewaySubnet' -VirtualNetwork $vnet

And then outputting the value of $gwsubnet in the console:

Name : GatewaySubnet Id : Etag : ProvisioningState : AddressPrefix : 10.1.1.0/24 IpConfigurations : null NetworkSecurityGroup : null RouteTable : null

Note that the Id property is null. This causes an error for a future step, e.g.:

$gwipconfig = New-AzureRmVirtualNetworkGatewayIpConfig -Name config1 -SubnetId $gwsubnet.Id -PublicIpAddressId $gwpip.Id

Gives the following error:

New-AzureRmVirtualNetworkGatewayIpConfig : Cannot validate argument on parameter 'SubnetId'. The argument is null or empty. Supply an argument that is not null or empty and then try the command again. At line:1 char:99 + ... nfig -SubnetId $gwsubnet.Id -PublicIpAddressId $gwpip.Id + ~~~~~~~~~~~~ + CategoryInfo : InvalidData: (:) [New-AzureRmVirtualNetworkGatewayIpConfig], ParameterBindingValidationException + FullyQualifiedErrorId : ParameterArgumentValidationError,Microsoft.Azure.Commands.Network.NewAzureVirtualNetworkGatewayIpConfigCommand

I'm struggling with how to have my subnet have an Id assigned to it. Is this something that I need to logout/login again to see? thanks for the help.

Solution

The problem you are having is that the subnet Id isn't created until you have created the virtual network.

When you run Get-AzureRmVirtualNetworkSubnetConfig all you create is a configuration to attach to New-AzureRmVirtualNetwork Once you have run that command it will connect to Azure, deploy the Vnet, create the subnet and at that state it will create a subnet Id.

The following code will show you what I mean...

$DNSNameLabel = "mydnsname"
$NetworkName = "MyNet"
$NICName = "MyNIC"
$PublicIPAddressName = "MyPIP"
$SubnetName = "MySubnet"
$SubnetAddressPrefix = "10.0.0.0/24"
$VnetAddressPrefix = "10.0.0.0/16"

$SingleSubnet = New-AzureRmVirtualNetworkSubnetConfig `
                -Name $SubnetName `
                -AddressPrefix $SubnetAddressPrefix

#At this point nothing is created, so there is no valid subnet id

$Vnet = New-AzureRmVirtualNetwork -Name $NetworkName `
                -ResourceGroupName $ResourceGroupName `
                -Location $LocationName `
                -AddressPrefix $VnetAddressPrefix `
                -Subnet $SingleSubnet

#vnet and subnet are created, both get an id and etag

 $vnet = Get-AzureRmVirtualNetwork -Name $NetworkName 
                -ResourceGroupName $ResourceGroupName 

$vnet.Subnets[0].Id 

Which will give

/subscriptions/{Subscription ID}/resourceGroups/MyResourceGroup/providers/Microsoft.Network/virtualNetworks/MyNet/subnets/MySubnet