An AS/400 cluster is defined to be a collection of complete systems that work together to provide a single, unified computing capability. A cluster is identified by a 10 character name. The cluster is comprised of one or more cluster nodes. A cluster node is an AS/400 system that is a member of a cluster. Each cluster node is identified by an 8 character cluster node identifier which is associated with a set of IP addresses representing an AS/400 system.
Cluster communications running over IP provides the communications path between cluster services on each node in the cluster. Cluster Resource Services requires that the loopback IP address on each node be active. The set of cluster nodes which have been configured for the cluster is referred to as the cluster membership list.
Whenever communication with a node is lost but node failure cannot be guaranteed, a cluster becomes partitioned. A cluster may be separated into multiple partitions. While partitioned, some cluster operations may be restricted. The restrictions are discussed in the introductions of the chapters describing the APIs.
High availability through clustering is accomplished through the implementation of resilient resources. A resilient resource is any system resource which is available on more than one node in the cluster. If a node in the cluster which is the primary access point for a particular set of resilient resources should fail, another node which is defined to be the backup for that set of resources, will become the access point. The definition of the relationship between the nodes associated with a set of resilient resources is found in the Cluster Resource Group (CRG) object. CRGs are distributed and coordinated across the nodes in the cluster. CRGs contain a recovery domain.
Recovery domain. A subset of nodes in a cluster grouped together to provide availability for one or more resources. A domain represents the nodes of the cluster where a cluster resource exists. See Cluster Resource Groups APIs for more information.
Cluster resource group. A grouping of cluster resources. The group describes a recovery domain and supplies the name of the cluster resource group exit program that manages the movement of an access point.
Cluster resource. A resource that is available on more than one cluster node.
Resilient resource. Resources that are recoverable by Cluster Resource Services. Two types of system resources that can be resilient are (1) objects being replicated between nodes and (2) applications using an IP address, which can be switched from one node to another.
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