Is there an easy way to call a migration from a controller for debugging purposes
Actually, the code isn't that hard to recreate from migration_tools. Here is my controller class:

&lt;?php

namespace Drupal\custom_migration\Controller;

use Drupal\Core\Controller\ControllerBase;
use Drupal\migrate\MigrateExecutable;
use Drupal\migrate\MigrateMessage;

class MigrateController extends ControllerBase {

  public function process() {

    $migration = \Drupal::service('plugin.manager.config_entity_migration')-&gt;createInstance('upgrade_d6_field_instance');
    $executable = new MigrateExecutable($migration, new MigrateMessage());
    $executable-&gt;import();


    return ['#markup' =&gt; 'Migrate Debugging'];
  }
}