Clustering, an overview

But what is clustering all about ? Basically there are 3 types of clusters, the most deployed ones are probably the Fail-over Cluster and the Load-balancing Cluster. High Performance Clusters are currently lesser used within the commercial market.

Fail-over Clusters consist of 2 or more network connected computers with a separate heartbeat connection between the 2 hosts. The Heartbeat connection between the 2 machines is being used to monitor whether all the services are still in use. As soon as a service on one machine breaks down the other machine tries to take over.

With load-balancing clusters the concept is that when a request for say a web-server comes in, the cluster checks which machine is the least busy and then sends the request to that machine.

Most of the time a Load-balancing cluster is also Fail-over cluster but with the extra load balancing functionality and often with more nodes.

The third variation of clustering is the High Performance Computing Cluster, this machine is being configured especially to give data centers that require extreme performance the performance they need. Beowulf's have been developed especially to give research facilities the computing speed they need. These kind of clusters also have some load-balancing features, they try to spread different processes to more machines in order to gain performance.

The underlying mechanism for distributing work is that different routines of a program are executed on different systems. Special programming libraries are used to synchronize the systems and pull together the results.

So where does openMosix fit into this picture ?, Actually openMosix is the alternative to the more classical Beowulf, but it's also complementary to this HPC technology.