Some nodes served headless Drupal and some nodes served with Drupal We are building a site that will be built and served via Drupal.  We want to have microsites that we want to share SOME of the content between the main site and the microsite.  We are thinking to build the microsites via Headless Drupal and use API from the main site.

The problems I see:

For example, node/2 should only be accessible on the microsite.  How would the main site which is not headless know that it can't access node/2?  Basically, some nodes will be served headless and some will be regular Drupal. 

Would it make things easier to just have the main site be headless as well?
Take a look at the Permissions by Term module.  You can add a term field that defines the site(s) the node is accessible by and limit access to content authors on the main site.

Your API for the microsites can use this to limit access by site as well.

If that one doesn't work, it's description lists another module that might work.