doRedis
is a foreach backend that is robust to node failure and that lets you add or remove worker nodes on the fly. Those are always useful features, but they are absolute requirements when you're running on EC2 spot instances that can shut down without warning. By using doRedis, you can move processing that would have required more reliable on-demand instances onto vastly cheaper spot instances.
If you're starting from scratch, the basic steps in running a simple personal cluster are: