external_node_products.php

  $test = drupal_lookup_path('source','upgrade');
  $upgrade_node_id = explode('/', $test)[1];
  $upgrade_node = node_load($upgrade_node_id);
  $upgrade_node_entity_wrapper = entity_metadata_wrapper('node', $upgrade_node);
  $upgrade_products = $upgrade_node_entity_wrapper->field_product->value();
  $proudct_ids = [];
  foreach($upgrade_products as $upgrade_product){
    $proudct_ids[] = $upgrade_product->sku;
  }