publicip-existing.json

{
  "$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "location": {
      "type": "string"
    },
    "publicIPAddressName": {
      "type": "string"
    },
    "publicIPAddressType": {
      "type": "string"
    },
    "dnsPrefix": {
      "type": "string"
    },
    "publicIpRGName": {
      "type": "string"
    }
  },
  "variables": {
    "publicIpId": "[resourceId(parameters('publicIpRGName'),concat('Microsoft.Network','/','publicIPAddresses'),parameters('publicIPAddressName'))]"
  },
  "resources": [],
  "outputs": {
    "resourceId": {
      "type": "string",
      "value": "[variables('publicIpId')]"
    },
    "fqdn": {
      "value": "[reference(variables('publicIpId'),providers('Microsoft.Network', 'publicIPAddresses').apiVersions[0]).dnsSettings.fqdn]",
      "type": "string"
    }
  }
}