Wackamole is a tool that helps with making a cluster highly available. It manages a bunch of virtual IPs that should be available to the outside world at all times, and ensures that exactly one machine within the cluster is listening on each virtual IP address that Wackamole manages. If it discovers that particular machines within the cluster are not alive, it will almost immediately ensure that other machines acquire the virtual IP addresses the down machines were managing. At no time will more than one connected machine be responsible for any virtual IP.
Ganglia is a scalable distributed monitoring system for high-performance computing systems such as clusters and grids. It is based on a hierarchical design targeted at federations of clusters. Ganglia is currently in use on over 500 clusters around the world and has scaled to handle clusters with 2000 nodes.