One Time Bulk Node Creation
Your options are:


Feeds module - You can check the doc here.
Export the content from source into csv or json. On the target (D8) either you can use Migrate module to handle the migration but requires custom coding. 
Create a json endpoint that will expose the content and in your target (D8) server consume that endpoint. You can then get the content by using Guzzle.


Example...

$request = Drupal::httpClient()-&gt;get($url);


See this page for more info.

P.S: I have no experience building with D8 yet but my suggestions above I guess is still applicable.