I have to migrate drupal-2-drupal content migration. My idea was to do with d2d migration module, it would be easy to do it. but after some search I find out it might not just with UI/or create prepare migration classes first and than do it with UI or drush.
My content is based on bit complex structure with paragraph and field collection items thats why I like to make classes. Still working on this solution.
If some one already working on it or examples are welcome.
One simple exampleis already here. https://www.drupal.org/node/2271181