Previously we had 1 publish and 1 dispatcher in staging, Now we have added one more publish(2) and dispatcher(2).
We have 2 dispatchers connected with load-balancer now.
Out of 6 sites, we have 2 sites are login-based sites. Planning to go with “/stickyConnections” for the authenticated site so that the dispatchers will serve from the same dispatcher & publisher.
In one of our sites, the logged-in user will create a favorite(collection of image path) and the favorite is stored under the /home/user/…/preferences/favorites/fov-1. Also, we store some information in the preferences node as well.
I have the below questions.
Where we need to add the “/stickyConnections“ property. In those two dispatchers farm or load-balancer.
How to sync the user preference & favorite node between two publishers.
Any other best approach apart from stickyconnection & node sync.
1. You should connect 1D with 1P and have the sticky sessions configured at load balancer level. This is a simple and recommended topology and it will be easier for you to manage sticky configuration at one single place.
2. For synchronizing content I will recommend you to use Sling Content Distribution. However, it will be better if you can manage the UGC outside AEM in an external storage to avoid any sync failures. But if not possible then go with sling content distribution. 
3. Along with the above you should also configure Encapsulated token authentication for achieving stateless authentication. This will help in continuing the login session in case one publisher goes down or becomes unresponsive.