Add Url Rule to Azure Application Gateway from a different ARM template - azure

Question

I have an resource group ARM template that I use to create an application gateway that is configured for url routing. It sends traffic to different Web Apps in that resource group based on url path rules. I deploy the base resource group ARM template, and then each web app has its own ARM template that setups a Web App on an App Service Plan. I am trying to figure out how to add a rule to an existing Url Path Map on an Application Gateway without defining the whole application gateway in every template. This way, I can simply add web apps and have them "register" on to the application gateway with a particular path rule.
I considered doing a linked template where my base template would have all of the shared resources (databases, app service plan, and app gateway), but even with a linked template, I don't think I can add a rule to the application gateway.
Update
So I modified my template by adding a reference to the existing application gateway, and then adding variables for the new BackEndPoolAddress and new Path Rule. It ends up like this (abbreviated to only relevant parts):
"variables": {
"appGateway": "[reference(concat('Microsoft.Network/applicationGateways/', 'appGateWay-', uniqueString(resourceGroup().id)), '2017-06-01')]",
"pathRule": {
"name": "[concat(parameters('websiteName'), '- RoutingRule')]",
"properties": {
"paths": [
"[parameters('routingRule')]"
],
"backendAddressPool": {
"id": "[concat(variables('appGateway').id, '/backendAddressPools/',parameters('websiteName'), 'BackEndPool')]"
},
"backendHttpSettings": {
"id": "[variables('appGateway').backendHttpSettingsCollection[0]]"
}
}
},
"backendPool": {
"name": "[concat(parameters('websiteName'), 'BackEndPool')]",
"properties": {
"IpAddress": "[reference(variables('webSiteName')).defaultHostName]"
}
}
},
"resources": [
...
{
"apiVersion": "2017-06-01",
"name": "[variables('appGateway').name]",
"type": "Microsoft.Network/applicationGateways",
"location": "[resourceGroup().location]",
"properties": {
"backendAddressPools": "[concat(variables('appGateway').backendAddressPools, variables('backendPool'))]",
"urlPathMaps": [
{
"name": "[variables('appGateway').urlPathMaps[0]]",
"pathRules": "[concat(variables('appGateway').urlPathMaps[0].pathRules, variables('pathRule'))]"
}
]
}
}
],
However I get a template validation error saying I can't use the Reference function in the Variables section. If I don't add it in the variables section, how can I build the correct paths for the pool and pathRule in my variables section?

Answer 1

you can achieve this using the reference() function, array manipulation and nested templates (might work even without those, worst case you will need them). example:
"outputs": {
"httpListeners": {
"type": "array",
"value": "[reference('application_gateway_id', '2018-08-01', 'Full').properties.httpListeners]"
}
}
Will return you array or httpListeners. you can get all the relevant application gateway properties and add new (additional) properties with the concat() and assign the result to the property (properties):
"httpListeners": "[concat(reference('application_gateway_id', '2018-08-01', 'Full').properties.httpListeners, variables('newListener'))]"
you just need to make sure 2 deployments dont start at the same time, one might overwrite the other

Answer 2

Here is the solution I finally ended up with using the Azure CLI. This script is idempotent and runs during my release process.
echo "Logging into AKS Cluster"
az aks get-credentials --resource-group $RESOURCEGROUP_NAME --name $AKSNAME
echo "Get the created service's ip address"
SERVICEIP=$(kubectl get service --namespace $AKSNAMESPACE $APPNAME-service -o jsonpath="{.status.loadBalancer.ingress[0].ip}")
echo "Creating backend pool - IP $SERVICEIP"
az network application-gateway address-pool create \
--gateway-name $APPGATEWAYNAME \
--resource-group $RESOURCEGROUP_NAME \
--name "$APPNAME-pool" \
--servers $SERVICEIP
echo "Creating probe"
az network application-gateway probe create \
--gateway-name $APPGATEWAYNAME \
--name "$APPNAME-probe" \
--path $APPPROBE \
--resource-group $RESOURCEGROUP_NAME \
--protocol Http \
--resource-group $RESOURCEGROUP_NAME \
--host-name-from-http-settings true
echo "Creating HTTP Settings"
az network application-gateway http-settings create \
--gateway-name $APPGATEWAYNAME \
--name "$APPNAME-settings" \
--port 80 \
--resource-group $RESOURCEGROUP_NAME \
--host-name-from-backend-pool \
--probe "$APPNAME-probe" \
--protocol Http
echo "Creating URL Path Map"
az network application-gateway url-path-map rule create \
--gateway-name $APPGATEWAYNAME \
--name "$APPNAME-rule" \
--paths $RULEPATH \
--path-map-name $RULENAME \
--resource-group $RESOURCEGROUP_NAME \
--http-settings "$APPNAME-settings" \
--address-pool "$APPNAME-pool"