publicIp-existing.json

{
  "$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "location": {
      "type": "string",
      "metadata": {
        "description": "Specifies the location of the public IP."
      }
    },
    "publicDnsName": {
      "type": "string",
      "metadata": {
        "description": "Specifies a unique public DNS prefix for the deployment. This will produce a FQDN of the form '<publicDnsName>.<location>.cloudapp.azure.com'. Up to 62 chars, digits or dashes, lowercase, should start with a letter: must conform to '^[a-z][a-z0-9-]{1,61}[a-z0-9]$'."
      }
    },
    "publicIpGroup": {
      "type": "string",
      "metadata": {
        "description": "Specifies the resource group which should contain the public IP."
      }
    },
    "publicIpName": {
      "type": "string",
      "metadata": {
        "description": "Specifies the resource name for the public IP. New IPs will take this name, while references to existing ones should be valid."
      }
    }
  },
  "variables": {
    "publicIpId": "[resourceId(parameters('publicIpGroup'),concat('Microsoft.Network','/','publicIPAddresses'),parameters('publicIpName'))]"
  },
  "resources": [],
  "outputs": {
    "resourceId": {
      "type": "string",
      "value": "[variables('publicIpId')]"
    },
    "fqdn": {
      "value": "[reference(variables('publicIpId'),providers('Microsoft.Network', 'publicIPAddresses').apiVersions[0]).dnsSettings.fqdn]",
      "type": "string"
    }
  }
}