2 Server Redundant Solution

Network setup

• Best scenario when both servers are on same LAN (subnet).
• If servers are on different LANs (subnets), VPNs between those servers have to be configured. Drawback - such setup management becomes too complicated.
• If servers are in the different countries (continents), it might cause latency problems which has negative influence on the speed of retrieving/instering data to the DB (loading statistics, trying to retrieve some data, searching for a sound file, etc. will longer than usually).
  
  

Workflow

• Both servers (S1 and S2) are identical.
• Both of them have two network interfaces - one for Virtual IP which is visible from outside, and one for local IP for interconnection (heartbeat monitoring, MySQL Replication)
• DB are synchronized over MySQL Replication
• LinuxHA heartbeat monitors servers, e.g.
  • When S1 fails - S2 sees that and after 10s (default) will take Virtual IP, e.g. will start to serve calls, it is done automatically
  • When S1 is back up - S2 returns Virtual IP to S1 and system starts to function in normal work flow (done automatically).
• VPN is necessary between servers if they are not on the same LAN