I'm currently running a CentOS VPS with some simple web/DB/VPN servers, but I'm planning to move to a vmWare Enterprise cloud based machine in the near future to improve availability, and I need to know how I should structure it further to ensure high availability and fail-over.
I'm running postgresql and two simple jetty webservers, one hidden behind OpenVPN - and I'm monitoring it with monit/munin.
Now I believe I should be trying to set up two nodes (? does that mean purchasing two different virtual machines) with fail-overs between them - PostgreSQLs streaming replication seems easy enough, and having a OpenVPN/webserver instance on each machine seems relatively simple - losing session state is probably fine (unless there's a way to share this) - my question is how do these two nodes interface, what sits before them and routes web traffic to each - or do you require a third machine, or is that built into vmWare to begin with?
I've also noticed some Cloud Hosts advertising HA SSL VPN, and I believe OpenVPN AS has a virtual appliance - should this replace my OpenVPN instance/s, or is there no need for this?
I imagine this might become more obvious once I actually get the servers, but for now I'm quite confused.