Communication between several servers.

Hello!

I want to organize communication between several servers (for example using some Main Sql Server).
Target: first friend on server "1.1.1.1" wants to invite second friend to new room. But second friend is on another "1.1.1.2" server (another physical machine with own Photon Server). First friend knows only ID of second friend.

My solution:
{
I think about using Main Sql Server to send/recieve requests to/from servers. And I can't just connect clients to sql server, because it would hard for main server have a lot of clients. It means that I have to change Photon Server to it would:
1)get IDs of current players (who now play on Photon Server)
2)send messages to main server with current IDs
3)recieve messages from main server and send these messages to current players (message smthg like "call method ConnectToFriendRoom(int ID, string AnotherPhotonServerIP, string AnotherRoomName)")

Main Sql Server has to recieve messages between connected servers with properties "ID" (of second friend), "AnotherPhotonServerIP" (of server where send friend has to connect), "AnotherRoomName".
}

Do I correctly made up the solution or there is another solution?
How to solve my target?