Clusters are groups of servers that are managed together and participate in workload management. A cluster can contain nodes or individual application servers. A node is usually a physical computer system with a distinct host IP address that is running one or more application servers. Clusters can be grouped under the configuration of a cell, which logically associates many servers and clusters with different configurations and applications with one another depending on the discretion of the administrator and what makes sense in their organizational environments.
Clusters are responsible for balancing workload among servers. Servers that are a part of a cluster are called cluster members. When you install an application on a cluster, the application is automatically installed on each cluster member.
Because each cluster member contains the same applications, one can distribute client tasks in distributed platforms according to the capacities of the different machines by assigning weights to each server.
In distributed platforms, assigning weights to the servers in a cluster improves performance and failover. Tasks are assigned to servers that have the capacity to perform the task operations. If one server is unavailable to perform the task, it is assigned to another cluster member. This reassignment capability has obvious advantages over running a single application server that can become overloaded if too many requests are made.
Node groups bound clusters. All cluster members of a given cluster must be members of the same node group.
A group of clusters can be defined as a core group. All of the application servers defined as a member of one of the clusters included in a core group are automatically members of that core group. Individual application servers that are not members of a cluster can also be defined as a member of a core group. The use of core groups enables WAS to provide high availability for applications that must always be available to end users. You can also configure core groups to communicate with each other using the core group bridge. The core groups can communicate within the same cell or across cells.
Clusters and workload management
Core group communications using the core group bridge service
Clusters and node groups
Setting up a high availability environment.
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