parametersLink option not passing parameters to templateLink - azure

Question

I am receiving an error:
"The value of deployment parameter 'appServiceName' is null."
Even though it is defined in the file obtained via parametersLink. I am never prompted so null is expected, but why am I never prompted? How do I properly pass parameters from a parametersLink file to a templateLink?
Master Template:
{
"$schema": "http://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
"contentVersion": "1.0.0.0",
"parameters": {
"rgName": {
"type": "string",
"metadata": {
"description": "Resource Group required in which to create App Service"
}
}
},
"variables": {},
"resources": [
{
"name": "LinkedAppServiceTemplate",
"type": "Microsoft.Resources/deployments",
"apiVersion": "2017-05-10",
"resourceGroup": "[parameters('rgName')]",
"properties": {
"mode": "Incremental",
"templateLink": {
"uri": "uri_to_template_file",
"contentVersion": "1.0.0.0"
},
"parametersLink": {
"uri": "uri_to_params_file",
"contentVersion": "1.0.0.0"
}
}
}
]
}
Linked Template:
{
"$schema": "http://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
"contentVersion": "1.0.0.0",
"parameters": {},
"variables": {},
"resources": [
{
"name": "[parameters('appServiceName')]",
"type": "Microsoft.Web/serverfarms",
"apiVersion": "2015-05-01",
"location": "[parameters('rgLocation')]"
}
]
}
Linked Params:
{
"$schema": "http://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
"contentVersion": "1.0.0.0",
"parameters": {
"appServiceName": {
"metadata": {
"description": "Name of the App Service to be created"
}
},
"rgLocation": {
"defaultValue": "eastus",
"metadata": {
"description": "Location of the resource group to be created"
}
}
}
}

Answer 1

You need to define the parameters in the file you've referred to as Linked Template:
Follow the tutorial on how to create linked templates as it will also show you how to pass the parameter from the main template to the linked template.
In this case, your Linked Template requires a parameter declaration in the parameters object.
"parameters": {
"appServiceName" : {
"type": "string",
"metadata" : {
"description": "This parameter needs to exist to pass from the link file"
}
}
}