[OpenSER-Users] Bigger OpenSER installation (2-5 Mio subs) and High Availability

Hello, I have done a project for a SIP provider who is rapidly growing. Designed as a SBC for about 50.000 subscribers at first, I setup a system with a high availability cluster (HA/DRBD) on 2 servers which had one single database on the DRBD volume. Failover works like a charm with only very limited downtime. Now we have to consider to scale the system to about 2-5 Mio subs, so I have to challenge with some things I cannot oversee at the moment. My question is: How do you deal with big installations? - how do you load balance the openser? Is it advisable put put some dedicated SIP hardware in front for load balancing? Or is the dispatcher module on a seperate machine sufficiant (again HA-issue)? - we have a portion of calls who have to go through mediaproxy (How do you load balance this?) - Do you face database issues? We think about setting up a database on 2 seperate servers. Is MySQL ok for this or do you use other DBMS? - Form your exoperience: Are there other things I have to consider? Best regards and thanks for your support. Peter