Author:- It’s the core AEM instance that is used by the authors/webmasters for designing content like carousels, home pages, banners, etc

Publisher:- Similar to the author, it is also the core AEM instance. The only difference is that it’s the actual server from where the content is served to the end-user unless it’s cached. When the author/webmaster finishes designing content he publishes the same and it is received at the publisher where it actually gets served to the end-users.

Dispatcher:- It’s like a front cache for the publisher. Whenever the publisher sends a response to the end-user for the first time it’s cached in the dispatcher and gets served from the dispatcher itself for the next time. Whenever an author updates content to the publisher sends an eviction request to the dispatcher for that content since it has been modified.

CDN:-It’s like a cache for a cache. The peculiar thing is that it’s specific to the location for eg. there is different CDN for America, Asia, Europe, China, etc. So the response from the dispatcher is caught ahead in the location-specific caches.