Many resources have properties that are only set once the resource is created, such as a public IP’s address or an ExpressRoute’s circuit service key. It is often helpful to have these as output from the deployment so they are available to any downstream automation tasks.
In this tutorial, you will deploy an ExpressRoute circuit, create a reference to the serviceKey
property on the newly deployed circuit, and provide that as the ARM deployment output.
An ExpressRoute circuit provides direct connectivity into Azure over a telecommunication provider’s network rather than traversing the Internet or a VPN. Once the circuit is created, the typical flow is to take the circuit’s service key to the telecommunications provider so they can enable it for your business connecivity.
open Farmer
open Farmer.Builders
let er = expressRoute {
name "my-test-circuit"
service_provider "Equinix"
peering_location "Frankfurt"
}
serviceKey
PropertyARM templates support expressions that are evaluated when the template is executed by ARM. These have many different capabilities, but in this case, we want to reference a newly deployed resource - the ExpressRoute circuit.
First, you can use the type and name of the resource to create a ResourceId
. Then, that ResourceId
can be used to build a reference
expression and retrieve a property of the resource.
// Build an ARM resourceId type for the circuit.
let erId = ResourceId.create(Arm.Network.expressRouteCircuits, er.Name)
// Use that ID to build a reference expression and get a property of the referenced resource.
let serviceKeyRef = ArmExpression.create ($"reference({erId.ArmExpression.Value}).serviceKey")
One or more outputs can be added to an arm
computation expression to generate outputs from the deployment. An output is created using the name for the output an an ArmExpression
, such as serviceKeyRef
created above.
arm {
location Location.WestEurope
add_resource er
output "er-service-key" serviceKeyRef
} |> Writer.quickWrite "custom-output"
This results in a template with an output named “er-service-key” that will contain the value of the serviceKey
property on the newly deployed ExpressRoute circuit.