The aem::instance resource definition is used to install and manage an AEM instance. An AEM installation is considered complete when the following steps have occurred:
- Unpacking the source file (See [documentation](https://docs.adobe.com/docs/en/aem/6-1/deploy/custom-standalone-install.html#Further options available from the Quickstart file).)
- Configuring the start script (See documentation.)
- Starting & Stopping the server, creating base repository.
Configuring an AEM installation where an unmanaged one exists is undefined (Theoretically it should work).