Azure resource manager template - property loops is not working keep getting error as copyindex is not expected - azure-resource-manager

Question

I am trying to deploy the Arm template using the properties copy loop as per the documentation available https://learn.microsoft.com/en-us/azure/azure-resource-manager/templates/copy-properties for loadbalancer and its not working. Template validation failed error as " language Expression property 'protocol' cant be evaluated.
If I remove loadbalancer rules copy and try iterating the healthprobes property alone its working.
{
"$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymenttemplate.json#",
"contentversion": "1.0.0.0",
"parameters": {
.......
"lbprobe": {
"type": "array",
"defaultValue": [
{
"name": "customAppPort",
"frontendPort": "8080",
"backendPort": "8888",
"protocolprobe": "tcp",
"protocol": "tcp"
},
{
"name": "httpsPort",
"frontendPort": "443",
"backendPort": "443",
"protocolprobe": "tcp",
"protocol": "tcp"
}
],
"metadata": {
"description": "description"
}
}
},
"functions": [],
"variables": {},
"resources": [
{
"name": "[parameters('lbname')]",
"type": "Microsoft.Network/loadBalancers",
"apiVersion": "2020-11-01",
"location": "[resourceGroup().location]",
"sku": {
"name": "Standard",
"tier": "Regional"
},
"properties": {
"frontendIPConfigurations": [
{
"name": "[parameters('lbfrontendip')]",
"properties": {
"privateIPAllocationMethod": "Dynamic",
"subnet": {
"id": "[resourceId('Microsoft.Network/virtualNetworks/subnets', 'testvnet-01', 'default')]"
}
}
}
],
"backendAddressPools": [
{
"name": "[parameters('lbbackendpool')]"
}
],
"copy": [
{
"name": "loadBalancingRules",
"count": "[length(parameters('lbprobe'))]",
"input": {
"name": "[parameters('lbprobe')[copyIndex('loadBalancingRules')].name]",
"properties": {
"frontendipconfiguration": {
"id": "[resourceid('microsoft.network/loadbalancers/frontendipconfigurations', parameters('lbname'), parameters('lbfrontendip'))]"
},
"backendaddresspool": {
"id": "[resourceid('microsoft.network/loadbalancers/backendaddresspools', parameters('lbname'), parameters('lbbackendpool'))]"
},
"protocol": "[parameters('lbprobe')[copyIndex('loadBalancingRules').protocol]]",
"frontendport": "[parameters('lbprobe')[copyIndex('loadBalancingRules').frontendPort]]",
"backendport": "[parameters('lbprobe')[copyIndex('loadBalancingRules').backendPort]]",
"enablefloatingip": false,
"idletimeoutinminutes": 5,
"probe": {
"id": "[resourceid('microsoft.network/loadbalancers/probes', parameters('lbname'),parameters('lbprobe')[copyIndex('loadBalancingRules')].name)]"
}
}
}
},
{
"name": "Probes",
"count": "[length(parameters('lbprobe'))]",
"input": {
"name": "[parameters('lbprobe')[copyIndex('Probes')].name]",
"properties": {
"protocol": "[parameters('lbprobe')[copyIndex('Probes')].protocolprobe]",
"port": "[parameters('lbprobe')[copyIndex('Probes')].frontendPort]",
"intervalInSeconds": 5,
"numberOfProbes": 2
}
}
}
]
}
}
],
"outputs": {}
}

Answer 1

We have tried the same code and can able to reproduce the above issue and identify the root cause.
Error Details:-
In your template in copy loadBalancingRules you are using the below:
"protocol": "[parameters('lbprobe')[copyIndex('loadBalancingRules').protocol]]",
"frontendport": "[parameters('lbprobe')[copyIndex('loadBalancingRules').frontendPort]]",
"backendport": "[parameters('lbprobe')[copyIndex('loadBalancingRules').backendPort]]",
Instead you should use the below:
"protocol": "[parameters('lbprobe')[copyIndex('loadBalancingRules')].protocol]",
"frontendport": "[parameters('lbprobe')[copyIndex('loadBalancingRules')].frontendPort]",
"backendport": "[parameters('lbprobe')[copyIndex('loadBalancingRules')].backendPort]",
OUTPUT DETAILS:-