server cluster
What is the different between server clustering and server replication?
Clusters are groups of servers which are tied together and configured for redundancy in the event that one member of the cluster fails. On properly configured clusters, with cluster compliant software, there is no interruption to the end users processing and in fact, they will not even be aware that an event has occurred. Clusters also have the ability to load balance between the cluster members. A cluster can receive a connection request from an end user and the cluster software will examine the CPU load on each of its members and assign the user to the least loaded machine in the cluster. End users do not need to know the hostnames of the individual cluster members. They connect to one cluster/hostname and the cluster software does the assignment automatically. There are several different types of clustering depending on what O/S your server machine is running (Windows, UNIX, OpenVMS, a few others...)
Server replication is a somewhat more generic term which refers to the complete mirroring of a server from one machine to another. Server replication can be used for a variety of functions. I have worked in installations where server replication was used to keep a mirror copy of a host at a remote location - sometimes hundreds of miles away - for the purposes of disaster recovery from such major events as earthquakes, floods ,etc (anything that might potentially knock your computer room down and prevent you from getting in).
In most type of clustering a full image of one machines is kept on all machines in the cluster to allow for failover in case one of the cluster members keels over. The act of creating these copies is referred to as replication. Whenever a change is made to one member of the cluster the propagation of this change to the other cluster members (thereby keeping them in sync) is referred to as replication.
I've glossed over some things but the above is a broad view of clustering and server replication.
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Open University Linux Server Cluster