[jcstk]

For a bit more detail:

The main isolate creates an Application instance that has N number of supervisors, one for each isolate. The isolates are launched and go thru their initialization steps, reporting back to their supervisor. The application completes its launch once all supervisors have reported back. It fails its launch if an isolate throws an error during initialization or does not hear back in a configurable timeout. Any inter-isolate messages sent during startup are queued until all isolates have completed startup.

Once the isolates are up and running, the main isolate doesn't do anything other than facilitate the inter-isolate message hub. Requests are delivered directly to the isolates running the web server.

When running automated tests, the default behavior is to run everything on the main isolate, since tests are run against a temporary database schema that only exists for the lifetime of the connection.