We have been using keepalived in Fedora Infrastructure for a while now. It’s a pretty easy to use and simple way to do some basic HA. Keepalived can keep track of which machine is “master” for a IP address and quickly fail over and back when moving that IP address around. You can also run scripts on state change. Keepalived uses VRRP and handles updating arp tables when IP addresses move around. It also supports weighting so you can prefer one or another server to “normally” have the master IP/scripts.
Right now we are keepalived on our main koji server pair. We have a koji01 and koji02. Normally 01 is primary/master and has the application IP address on it so all traffic goes to it. If for some reason it was turned off, the keepalived on 02 would see that and take the IP address and run a script to become master. If 01 came back up, 02 would see that and transfer back to it. Right now we have the scripts setting up on the secondary server a bunch of cron jobs (garbage collection) and kojira (the process that regenerates build roots).
We are also using keepalived on some new paired postgresql instances we are working on. More on that in a later blog post. If you need simple HA with a IP address and script(s), keepalived does a banner job.