code: func extractResourceGroupByProviderID(providerID string) (string, error) {
  	matches := resourceGroupRE.FindStringSubmatch(providerID)
  	if len(matches) != 2 {
  		return "", ErrorNotVmssInstance
  	}
  
  	return matches[1], nil
  }
docs: // extractResourceGroupByProviderID extracts the resource group name by vmss node's ProviderID.