Centos – Redhat cluster Vs Pacemaker Vs Gluster Vs Sheepdog

you can use manual fencing for testing. search for fence_manual in this doc

this will not disable fencing, but nothing will happen when you not want to.

You seem somewhat stuck with the DRBD replication. I would think this is because it does not suit your needs. It replicates block devices and is quite bandwidth-intensive (although link compression might alleviate that quite a bit). Check out if you would not be happier with replication at a higher level - like MySQL replication mechanisms for the databases and something like lsyncd for the filesystems.

Gluing it together with stuff from the linux-ha project or setting up a semiautomatic or manual failover mechanism in conjunction with some monitoring is surely a bit of work, but should give you what you want in the long run.

Of course, you still would need an encrypted tunnel for the traffic, but I do not understand your reluctance to using OpenVPN - as the tunnel is just there for the sake of a backup/standby system and you would have either a witness (in a HA setup with automatic failover) or a monitoring system (in a setup with monitoring) which is independent from the presence of the tunnel, you would not have any failovers on tunnel outages and just get the alarms to fix the tunnel upon outage (which is of course necessary, otherwise you lose the capability to do a failover to an up-to-date standby system).