Centos – Disable fencing in RedHat Cluster

Power

Use Switched PDUs so that you can turn servers and switches on and off out-of-band. This is OS- and device-independent, which will greatly simplify the configuration and logic that powers things on and off. If your servers all have network-enabled IPMI interfaces, you can use those instead. I would recommend against trying to turn things on and off using higher-level things like wake-on-LAN.

Power up/down Logic

This could take many forms. Some clustering software (such as Moab) has a solution for this built in. Otherwise, you can write some script with the following pseudocode:

1. Check overall cluster load
2. If cluster load > threshold1, turn on some nodes
3. If cluster load < threshold2, turn off some nodes

Put that in cron and have it run every half hour.

Clustering Software Stack

Obviously, you'll need to make sure your clustering software stack can deal with these devices going up and down all the time. Do a lot of testing here, consider obscure timing issues (booting takes time) and any race conditions that will creep up in the power up/down logic you use.