How to port active configuration to module configuration Scenario: I have a website which was initially developed with a single site (A) in mind. Now, because reasons, I need to make this a multi-site setup (A &amp; B). So, I have functionality in A I want to share with B. We built A with all config exported to it's config sync folder, which means all config is intertwined. 

Problem: How would I go about converting all sharable configuration to modules, which would allow me to maintain the modules from one codebase in both A &amp; B? Putting everything into module_foobar/config/install/ will not work that easily for A, since it already has that config in it's active config.
Use Features: It basically does exactly what you want, it turns your existing configuration into a module_foobar/config/install/ 

Be aware though that Features merges config (it does add and update existing config, but it does not remove/delete unused config like core configuration management).