Open Source, High Availability resource manager suitable for both small and large clustershttp://clusterlabs.org/
Pacemaker is a cluster resource manager.
It achieves maximum availability for your cluster services (aka. resources) by detecting and recovering from node and resource-level failures by making use of the messaging and membership capabilities provided by your preferred cluster infrastructure (either OpenAIS or Heartbeat).
It can do this for clusters of practically any size and comes with a powerful dependency model that allows the administrator to accurately express the relationships (both ordering and location) between the cluster resources.
Virtually anything that can be scripted can be managed as part of a Pacemaker cluster.