Attach_Existing_NIC_to_Stopped_VM_then_Remove_Other_NIC.ps1

# https://docs.microsoft.com/en-us/azure/virtual-machines/windows/multiple-nics

# "Stop" the VM first

$subscriptionname = "yoursubscription"
$resourcegroupname = "yourresourcegroup"
$vmname = "yourvmname"
$vnetname = "vnetname"
$subnetname = "subnetname"
$wantednicname = "newnicname"
$unwantednicname = "oldnicname"

# ---------------
# AUTHENTICATION
# ---------------
Login-AzureRmAccount
Select-AzureRmSubscription -SubscriptionName $subscriptionname

$vm = Get-AzureRmVm -Name $vmname -ResourceGroupName $resourcegroupname

# Get info for the back end subnet
$vnet = Get-AzureRmVirtualNetwork -Name $vnetname -ResourceGroupName $resourcegroupname
$subnet = $vnet.Subnets|?{$_.Name -eq '$subnetname'}

# Get the ID of the new virtual NIC and add to VM
$nic = (Get-AzureRmNetworkInterface -ResourceGroupName $resourcegroupname -Name $wantednicname).Id

# List existing NICs on the VM and find which one is primary
$vm.NetworkProfile.NetworkInterfaces

# Add second NIC (expect an eror here - "Virtual machine Jayan-AEMReporting-Publish1 must have one network interface set as the primary.")
Add-AzureRmVMNetworkInterface -VM $vm -Id $nic | Update-AzureRmVm -ResourceGroupName $resourcegroupname

# List existing NICs on the VM and find which one is primary
$vm.NetworkProfile.NetworkInterfaces

# Set NIC 2 to be primary
$vm.NetworkProfile.NetworkInterfaces[1].Primary = $true

# Verify
$vm.NetworkProfile.NetworkInterfaces

# Get the NIC to be removed
$nic2 = (Get-AzureRmNetworkInterface -ResourceGroupName $resourcegroupname -Name $unwantednicname).Id

# Remove it
Remove-AzureRmVMNetworkInterface -VM $vm -NetworkInterfaceIDs $nic2

# Verify
$vm.NetworkProfile.NetworkInterfaces

# Update the VM state in Azure (this takes time)
Update-AzureRmVM -VM $vm -ResourceGroupName $resourcegroupname

# Verify
$vm.NetworkProfile.NetworkInterfaces

# Enable "accelerated networking"
$nic = Get-AzureRmNetworkInterface -ResourceGroupName $resourcegroupname -Name $wantednicname
$nic.EnableAcceleratedNetworking = $true
$nic | Set-AzureRmNetworkInterface

# You can now delete the removed NIC from the Azure Portal