Drupal 8 master site for managing customer Drupal 8 sites? Possible? Question: Drupal 8 master site for managing customer Drupal 8 sites? Possible?

Goal:

There will be a master drupal 8 site developed for managing basic business modules.
These basic business modules should be available to all customer sites. (shared)
Also the user roles and users must be shared.

There is no 1 shared codebase.
There is also the need for customer site-specific modules that can be installed. 
So log in with the credentials from the master site at a customer site is also needed.

A picture of the goal:



Research:

I have researched several solutions like:


Multi-Site
Domain Access


These solutions I have explored share the same code base.

Expected solution:

The solution that I want to achieve is no shared code base, each project has its own code base, 
but also the modules of the master Drupal 8 installation.
This would come as basic business modules required for each customer site like 
autopath and xmlsitemap. 
So if I install a module on the master site must also be available in the customer site.

The master site code may be shared thus not 100%, but also not completely independent from each other.

Is that possible ? Are they better/other methods for achieving this goal ?
It sounds very much like you'll need two solutions. For sharing the code and parts of the configuration a distribution/install_profile makes sense (https://www.drupal.org/docs/8/creating-distributions). When you make changes to the distribution you'll need to write hook_update_N functions to make these changes on the sites that are using it. So updating a customer site becomes the number problem of deploying coding and running update.php (or doing a cli command).

With respect to sharing roles and users this I might look to do something different. Maybe integrate with a third party identity services that allows you to share the identities across your sites. The roles can be deployed as configuration as part of the install profile. Buried somewhere in this presentation https://events.drupal.org/dublin2016/sessions/no-compromises-%E2%80%93-react-relay-and-graphql-drupal-8 is something about integrating Drupal 8 with an identify provider. And there's also things like https://www.drupal.org/project/openid_connect