Clustering terminology

Node. Refers to the individual system that is part of a cluster. Each node in the cluster has its own local resources. However, the cluster also has common resources, such as a common data storage. These common resources are accessible to each node in the cluster.

Load Balancing. Is the ability to switch between the locations where similar requests are handled. For example, a request for a database connection might be handled on any one of four different servers in a cluster. Deciding which server handles the request depends on the load-balancing logic.

Availability. Refers to the quality of the system's response to process a request, denoting the amount of time that an application or system is available to perform work. Availability is typically measured in percentage uptime.

High Availability. Is defined as support to backup services in the case of a system or node failure. A system with high availability uses load balancing so that all requests are routed to one or more preferred servers until one of the servers becomes unavailable, and then routed to another server that is still operational.

Failover. Is the ability for a request that is being serviced, to have a high availability switchover to another node without disruption of the service. A successful failover means to transfer the service without any intervention by client or manual process.

Scalability. Denotes capability of a system to scale up to provide sustained system availability and throughput, without unacceptable degradation under increase in load. The increase in load could be due to increase in the number of users accessing the application, or in the volume or size of user transactions or actions.

Reliability. Is the ability of a system to perform its required functions and sustain a requested service under stated conditions for a specified period of time.

Throughput. It is the rate of information arriving at, and possibly passing through, a particular point in a network system. The rate at which a processor can work expressed in instructions per second or jobs per hour or some other unit of performance.

Horizontal Cluster. This refers to multiple installations of Progress OpenEdge BusinessManager (herewith referred to as OpenEdge BusinessManager or BusinessManager), each hosting a cluster node, running in the same physical computer or multiple computers, but each BusinessManager installation is part of the same cluster and runs homogeneously.

Vertical Cluster. This refers to a single installation of BusinessManager hosting multiple cluster nodes, running in the same physical machine. A vertical cluster could be part of a horizontal cluster that is, a cluster having three nodes could have two nodes running in the same computer (vertical cluster) and the third node in a different computer (horizontal cluster).