How to process an http request with a controller?
Ok, my problem was the serialization. To recover my node object in my function of POST, I should deserialize the json with the function:

 $data = \GuzzleHttp\json_decode( $request-&gt;getContent(), TRUE);
 $serializer = \Drupal::service('serializer');
 $node = $serializer-&gt;deserialize($data, \Drupal\node\Entity\Node::class, 'json');

 $new_node = Node::create(array(
   'type' =&gt; $node-&gt;bundle(),
   'title' =&gt; $node-&gt;title,
   'langcode' =&gt; $node-&gt;language()-&gt;getId(),
   'uid' =&gt; '1',
   'status' =&gt; 1,
   'body' =&gt; $node-&gt;get('body'),
 ));

 $new_node-&gt;save();


Now, I can manipulate my node like I want in my other website.