Default Values in ARM templates when using Template Specs - azure

Question

We have implemented Template Specs for our ARM deployments to Azure a while ago and we drastically decreased the amount of work by doing that. The next thing we're trying to achieve is to start implementing Default Values in template specs, so we do not have to specify all parameters that are the same in all our projects in the parameter files. In case we do want to override the default, we can of course specify the parameter in the parameter file.
We worked with this already in the past with templates and parameter files, but I can't get this to work with Template Specs.
As an example, I'm trying to deploy an App Service Plan like this:
Template Spec:
{
"$schema": "http://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
"contentVersion": "1.0.0.0",
"parameters": {
"appServicePlanSettings": {
"type": "object",
"defaultValue": {
"isHypervContainerPlan": false
}
},
"resourceNameAndTagSettings": {
"type": "object"
}
},
"variables": {
"appServicePlanName": "[concat('o', parameters('appServicePlanSettings').nameAbbr, parameters('resourceNameAndTagSettings').environmentType, parameters('resourceNameAndTagSettings').resourceGroupNumber, parameters('resourceNameAndTagSettings').solutionNameAbbr, parameters('resourceNameAndTagSettings').locationAbbr)]"
},
"resources": [
{
"comments": "App Service Plans",
"condition": "[parameters('appServicePlanSettings').deploy]",
"apiVersion": "2020-09-01",
"type": "Microsoft.Web/serverfarms",
"name": "[variables('appServicePlanName')]",
"location": "[resourceGroup().location]",
"tags": {
"_Purpose": "[parameters('appServicePlanSettings').tagValuePurpose]",
"CostCenter": "[parameters('resourceNameAndTagSettings').tagValueCostCenter]",
"EnvironmentType": "[parameters('resourceNameAndTagSettings').tagValueEnvironmentType]",
"Owner": "[parameters('resourceNameAndTagSettings').tagValueOwner]"
},
"kind": "[parameters('appServicePlanSettings').kind]",
"sku": {
"name": "[parameters('appServicePlanSettings').sku]",
"size": "[parameters('appServicePlanSettings').sku]",
"tier": "[parameters('appServicePlanSettings').skuTier]"
},
"properties": {
"hyperV": "[parameters('appServicePlanSettings').isHypervContainerPlan]",
"perSiteScaling": "[parameters('appServicePlanSettings').perSiteScaling]",
"reserved": "[parameters('appServicePlanSettings').isLinuxOS]"
},
"dependsOn": []
}
],
"outputs": {}
}
Main Template:
{
"$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
"contentVersion": "1.0.0.0",
"parameters": {
"appServicePlanSettings": {
"type": "array"
},
"dateTime": {
"type": "string",
"defaultValue": "[utcNow()]"
},
"resourceNameAndTagSettings": {
"type": "object"
},
"templateSpecSettings": {
"type": "object"
}
},
"resources": [
{
"comments": "Apps - App Service Plans",
"type": "Microsoft.Resources/deployments",
"apiVersion": "2020-06-01",
"name": "[concat('Deploy-', parameters('appServicePlanSettings')[copyIndex()].nameAbbr, parameters('resourceNameAndTagSettings').environmentType, parameters('resourceNameAndTagSettings').resourceGroupNumber, parameters('resourceNameAndTagSettings').solutionNameAbbr, parameters('resourceNameAndTagSettings').locationAbbr, '-', parameters('dateTime'))]",
"copy": {
"name": "appServicePlanCopy",
"count": "[length(parameters('appServicePlanSettings'))]"
},
"properties": {
"mode": "Incremental",
"templateLink": {
"id": "[concat('/subscriptions/', parameters('templateSpecSettings').templateSpecSubscriptionId, '/resourceGroups/', parameters('templateSpecSettings').templateSpecResourceGroupName, '/providers/Microsoft.Resources/TemplateSpecs/', parameters('templateSpecSettings').appServicePlan.name, '/versions/', parameters('templateSpecSettings').appServicePlan.version)]"
},
"parameters": {
"appServicePlanSettings": {
"value": "[parameters('appServicePlanSettings')[copyIndex()]]"
},
"resourceNameAndTagSettings": {
"value": "[parameters('resourceNameAndTagSettings')]"
}
}
},
"dependsOn": []
}
],
"outputs": {}
}
Parameter File:
{
"$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentParameters.json#",
"contentVersion": "1.0.0.0",
"parameters": {
"appServicePlanSettings": {
"value": [
{
"comments": "App Service Plan 1",
"deploy": true,
"nameAbbr": "Asp",
"isLinuxOS": false,
"isHypervContainerPlan": false,
"perSiteScaling": false,
"tagValuePurpose": "Test",
"kind": "app",
"sku": "P1v2",
"skuTier": "PremiumV2"
}
]
},
"resourceNameAndTagSettings": {
"value": {
"environmentType": "dev",
"locationAbbr": "europe",
"resourceGroupNumber": "001",
"solutionNameAbbr": "test",
"tagValueCostCenter": "123",
"tagValueEnvironmentType": "Development",
"tagValueOwner": "me"
}
},
"templateSpecSettings": {
"value": {
"templateSpecResourceGroupName": "XXX",
"templateSpecSubscriptionId": "XXX",
"appServicePlan": {
"name": "appServicePlanTest",
"version": "1.2"
}
}
}
}
}
This deploys just fine.
But if I leave out:
"isHypervContainerPlan": false,
in the parameter file, the deployment will fail with this message:
Unable to process template language expressions for resource '...' at
line '24' and column '9'. 'The language expression property
'isHypervContainerPlan' doesn't exist, available properties are
'comments, deploy, nameAbbr, isLinuxOS, perSiteScaling,
tagValuePurpose, kind, sku, skuTier'.
Why would it fail on this error if the defaultValue is set in the Template Spec parameters section?
What am I missing here or are defaultValues not supported with Template Specs?

Answer 1

A defaultValue on a parameter is only used if no value is supplied. Put another way, you can you either use the defaultValue for a parameter or supply a value, not both, nor any combination of the two.
Your templateSpec expects a complex object for the appServicePlanSettings parameter. That object needs to have all of the properties referenced by the serverFarm resource being deployed. You're supplying a value for that param, but you're also omitting one of the properties from that parameter, and that's the property that's being flagged in the error message.
To see this in action in another way, put that property back into your param file and remove a different one, you'll see a similar error... or you could just not supply a param value at all for the ``appServicePlanSettings``` and then the defaultValue will be used.

Answer 2

I've been testing with the 'defaultValue'.
I have also tested with this setup:
Template:
{
"$schema": "http://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
"contentVersion": "1.0.0.0",
"parameters": {
"appServicePlanSettings": {
"type": "object",
"defaultValue": {
"isHypervContainerPlan": false,
"isLinuxOS": false,
"perSiteScaling": false
}
},
"resourceNameAndTagSettings": {
"type": "object"
}
},
"variables": {
"appServicePlanName": "[concat('o', parameters('appServicePlanSettings').nameAbbr, parameters('resourceNameAndTagSettings').environmentType, parameters('resourceNameAndTagSettings').resourceGroupNumber, parameters('resourceNameAndTagSettings').solutionNameAbbr, parameters('resourceNameAndTagSettings').locationAbbr)]"
},
"resources": [
{
"comments": "App Service Plans",
"condition": "[parameters('appServicePlanSettings').deploy]",
"apiVersion": "2020-09-01",
"type": "Microsoft.Web/serverfarms",
"name": "[variables('appServicePlanName')]",
"location": "[resourceGroup().location]",
"tags": {
"_Purpose": "[parameters('appServicePlanSettings').tagValuePurpose]",
"CostCenter": "[parameters('resourceNameAndTagSettings').tagValueCostCenter]",
"EnvironmentType": "[parameters('resourceNameAndTagSettings').tagValueEnvironmentType]",
"Owner": "[parameters('resourceNameAndTagSettings').tagValueOwner]"
},
"kind": "[parameters('appServicePlanSettings').kind]",
"sku": {
"name": "[parameters('appServicePlanSettings').sku]",
"size": "[parameters('appServicePlanSettings').sku]",
"tier": "[parameters('appServicePlanSettings').skuTier]"
},
"properties": {
"hyperV": "[parameters('appServicePlanSettings').isHypervContainerPlan]",
"perSiteScaling": "[parameters('appServicePlanSettings').perSiteScaling]",
"reserved": "[parameters('appServicePlanSettings').isLinuxOS]"
},
"dependsOn": []
}
],
"outputs": {}
}
Parameters:
{
"$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentParameters.json#",
"contentVersion": "1.0.0.0",
"parameters": {
"appServicePlanSettings": {
"value": {
"comments": "App Service Plan 1",
"deploy": true,
"nameAbbr": "Asp",
"isLinuxOS": "",
"isHypervContainerPlan": "",
"perSiteScaling": "",
"tagValuePurpose": "Test",
"kind": "app",
"sku": "P1v2",
"skuTier": "PremiumV2"
}
},
"resourceNameAndTagSettings": {
"value": {
"environmentType": "dev",
"locationAbbr": "europe",
"resourceGroupNumber": "001",
"solutionNameAbbr": "test",
"tagValueCostCenter": "123",
"tagValueEnvironmentType": "Development",
"tagValueOwner": "me"
}
},
"templateSpecSettings": {
"value": {
"templateSpecResourceGroupName": "oGen1Weu1PrdMng001",
"templateSpecSubscriptionId": "130176f8-513a-4869-9db3-7c46d0e25159",
"appServicePlan": {
"name": "appServicePlanTest",
"version": "1.2"
}
}
}
}
}
Which also doesn't work when I do not specify "isHypervContainerPlan" in the parameter file, I thought we tested this, but apparently not good enough...
The only thing that works is defining:
"isHypervContainerPlan": "",
in the parameter file, thus not specifying a value. Which is not desirable, because then still all parameters have to be defined, even when I do not want to override the defaults.
So, the solution in the end has become the following (the main template remains the same):
Template Spec:
{
"$schema": "http://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
"contentVersion": "1.0.0.0",
"parameters": {
"appServicePlanSettings": {
"type": "object"
},
"resourceNameAndTagSettings": {
"type": "object"
}
},
"variables": {
"appServicePlanName": "[concat('o', parameters('appServicePlanSettings').nameAbbr, parameters('resourceNameAndTagSettings').environmentType, parameters('resourceNameAndTagSettings').resourceGroupNumber, parameters('resourceNameAndTagSettings').solutionNameAbbr, parameters('resourceNameAndTagSettings').locationAbbr)]",
"appServicePlanSettings": {
"isHypervContainerPlan": false,
"isLinuxOS": false,
"kind": "app",
"nameAbbr": "Asp",
"perSiteScaling": false
}
},
"resources": [
{
"comments": "App Service Plans",
"condition": "[parameters('appServicePlanSettings').deploy]",
"apiVersion": "2020-09-01",
"type": "Microsoft.Web/serverfarms",
"name": "[variables('appServicePlanName')]",
"location": "[resourceGroup().location]",
"tags": {
"_Purpose": "[parameters('appServicePlanSettings').tagValuePurpose]",
"CostCenter": "[parameters('resourceNameAndTagSettings').tagValueCostCenter]",
"EnvironmentType": "[parameters('resourceNameAndTagSettings').tagValueEnvironmentType]",
"Owner": "[parameters('resourceNameAndTagSettings').tagValueOwner]"
},
"kind": "[if(contains(parameters('appServicePlanSettings'), 'kind'), parameters('appServicePlanSettings').kind, variables('appServicePlanSettings').kind)]",
"sku": {
"name": "[parameters('appServicePlanSettings').sku]",
"size": "[parameters('appServicePlanSettings').sku]",
"tier": "[parameters('appServicePlanSettings').skuTier]"
},
"properties": {
"hyperV": "[if(contains(parameters('appServicePlanSettings'), 'isHypervContainerPlan'), parameters('appServicePlanSettings').isHypervContainerPlan, variables('appServicePlanSettings').isHypervContainerPlan)]",
"perSiteScaling": "[if(contains(parameters('appServicePlanSettings'), 'perSiteScaling'), parameters('appServicePlanSettings').perSiteScaling, variables('appServicePlanSettings').perSiteScaling)]",
"reserved": "[if(contains(parameters('appServicePlanSettings'), 'isLinuxOS'), parameters('appServicePlanSettings').isLinuxOS, variables('appServicePlanSettings').isLinuxOS)]"
},
"dependsOn": []
}
],
"outputs": {}
}
And if I don't specify these values now in the parameter file, the value configured in the variable section will be used:
{
"$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentParameters.json#",
"contentVersion": "1.0.0.0",
"parameters": {
"appServicePlanSettings": {
"value": [
{
"comments": "App Service Plan 1",
"deploy": true,
"nameAbbr": "Asp",
"tagValuePurpose": "Test",
"kind": "app",
"sku": "P1v2",
"skuTier": "PremiumV2"
}
]
},
"resourceNameAndTagSettings": {
"value": {
"environmentType": "dev",
"locationAbbr": "europe",
"resourceGroupNumber": "001",
"solutionNameAbbr": "test",
"tagValueCostCenter": "123",
"tagValueEnvironmentType": "Development",
"tagValueOwner": "me"
}
},
"templateSpecSettings": {
"value": {
"templateSpecResourceGroupName": "XXX",
"templateSpecSubscriptionId": "XXX",
"appServicePlan": {
"name": "appServicePlanTest",
"version": "1.2"
}
}
}
}
}