Alright, so I hope my post helps someone looking for a way to make sure content is always added to master server behind a load-balancer.
Our current typical setup has Drupal7 on 4 servers:
Prodweb1 - File system | Master
Prodweb2 - File system | Slave
Proddb1 - Database | Master
Proddb2 - Database | Slave
Using Lsyncd to push content from Prodweb1 to Prodweb2, and from Proddb1 to Proddb2
Both File systems are pulling content from Proddb1 ONLY. Proddb2 is just a realtime backup of the master DB.
Now both Prodweb1 and Prodweb2 are behind a load balancer, so the typical issue we get is that authors logs in on www.mysite/user and add their content. The content is stored in the DB, so all good, but if the load balancer logs the user on Prodweb2, then the images / files are saved in sites/default/files/ on Prodweb2. Now when lsync crawls, it sees new files on Prodweb2 but not on Prodweb1, so it deletes those files totally.
To overcome this issue, here is what I did:
1. At my domain registrar (godaddy), created a new subdomain let's call it admin and pointed admin.mysite to the IP of Prodweb1 (not the load balancer).
2. I made a change in the settings.php file located at sites/default/settings.php to read the subdomain of the site, (I already have .htaccess configured to point non-www visitors to www), and change $base_url and $cookie_domain as follows: