Suppose you really need a highly available service. Normally you would put a load balancer in front of a server farm. But what happens when the load balancer fails? Well, we could have to load balancers, one which is actually active and the second one kicking in when first one fails.

We could have two servers or two VMs that are in the same VLAN, they both have their own IP, they are able to communicate/broadcast to each other and there’s a third IP that is shared between the two servers/VMs. One of them is MASTER the other one is BACKUP.

For a test setup I used CentOS 7, you could use your own favorite distro. I’ve set-up on my test machines with 192.168.6.110/24 and 192.168.6.120/24 as the machine’s IPs. I’m going to set two clustered/highly available IPs 192.168.7.100/24 and 192.168.7.110/24. Notice they’re from different classes, machine’s IPs could be anything as long as the two machines can communicate with each other. The default gateway on the two ...