Just want to pass this by people in case there's anything I should be aware of or missing something.
2 Servers each with local DB.
Server A - Multisite - Master (Multi-DB)
Server B - Multisite & BuddyPress - Subsite
User Synchronization plugin is install and syncing users from Master to Subsite is working.
When user changes the password on Subsite through BuddyPress frontend user then has different passwords on Master & Subsite as I assume user sync is one way only.
So moved Subsite database onto Server A into db_global using different table prefix.
On Server B added the following to wp-config
When user on Server B changes password in Buddypress frontend can now access Server A & Server B with the same new password which is what I wanted to achieve.
I've disabled user signups on Server B and allowed blog creation for existing users only.
Next steps would then to setup Multi-DB for Server B and set both servers as MySQL Master-Master replication so that Server A & Server B can read/write to DB locally.
Server A & Server B have two different functions and thus wanted to spread the load in regards to DB, Web, Plugins, etc but give features located on both to all users.
Thoughts would be appreciated.