Glossary

clusterware

A software that manages the operations of the members of a cluster as a system. It allows one to define a set of resources and services to monitor through a heartbeat mechanism between cluster members and to move these resources and services to a different member in the cluster as efficiently and transparently as possible.

hardware cluster

A hardware cluster is a collection of computers that provides a single view of network services (for example: an IP address) or application services (for example: databases, Web servers) to clients of these services. Each node in a hardware cluster is a standalone server that runs its own processes. These processes can communicate with one another to form what looks like a single system that cooperatively provides applications, system resources, and data to users.

A hardware cluster achieves high availability and scalability through the use of specialized hardware (cluster interconnect, shared storage) and software (health monitors, resource monitors). (The cluster interconnect is a private link used by the hardware cluster for heartbeat information to detect node death.) Due to the need for specialized hardware and software, hardware clusters are commonly provided by hardware vendors such as Sun, HP, IBM, and Dell. While the number of nodes that can be configured in a hardware cluster is vendor dependent, only two nodes are required for Oracle Application Server high availability. Hence, this document assumes a two-node hardware cluster for high availability solutions employing a hardware cluster.

network hostname

Network hostname is a name assigned to an IP address either through the /etc/hosts file (on UNIX), C:\WINDOWS\system32\drivers\etc\hosts file (on Windows), or through DNS resolution. This name is visible in the network that the system which it refers to is connected. A system may have the same network hostname and physical hostname. However, although a system has only one physical hostname, it may have multiple network hostnames. Thus, a system's network hostname may not always be its physical hostname.

physical hostname

This guide differentiates between the terms physical hostname and network hostname. This guide uses physical hostname to refer to the "internal name" of the current system. The physical hostname is the name returned by the hostname command.

The physical hostname is used by Oracle Application Server to reference the local host. During installation, the installer automatically retrieves the physical hostname from the current system and stores it in the Oracle Application Server configuration metadata on disk.

shared storage

Although each node in a hardware cluster is a standalone server that runs its own set of processes, the storage subsystem required for any cluster-aware purpose is usually shared. Shared storage refers to the ability of the cluster to be able to access the same storage, usually disks, from either node in the hardware cluster. While the nodes have equal access to the storage, only one node, the primary node, has active access to the storage at any given time. The hardware cluster's software grants the secondary node access to this storage if the primary node fails.

In OracleAS Cold Failover Cluster (Middle-Tier) environments, you can install the Oracle home directory on a shared storage system or on a local storage of each node in the hardware cluster.

virtual hostname

Virtual hostname is a network addressable hostname that maps to one or more physical systems through a load balancer or a hardware cluster. For load balancers, the name "virtual server name" is used interchangeably with virtual hostname in this book. A load balancer can hold a virtual hostname on behalf of a set of servers, and clients communicate indirectly with the systems using the virtual hostname. A virtual hostname in a hardware cluster is a network hostname assigned to a cluster virtual IP. Because the cluster virtual IP is not permanently attached to any particular node of a cluster, the virtual hostname is not permanently attached to any particular node either.

Note that when the term "virtual hostname" is used in this document, it is assumed to be associated with a virtual IP address. In cases where just the IP address is needed or used, it will be explicitly stated.

virtual IP

Also, cluster virtual IP and load balancer virtual IP. Generally, a virtual IP can be assigned to a hardware cluster or load balancer. To present a single system view of a cluster to network clients, a virtual IP serves as an entry point IP address to the group of servers which are members of the cluster. A virtual IP can be assigned to a server load balancer or a hardware cluster.

A hardware cluster uses a cluster virtual IP to present to the outside world the entry point into the cluster (it can also be set up on a standalone system). The hardware cluster's software manages the movement of this IP address between the two physical nodes of the cluster while clients connect to this IP address without the need to know which physical node this IP address is currently active on. In a typical two-node hardware cluster configuration, each system has its own physical IP address and physical hostname, while there could be several cluster IP addresses. These cluster IP addresses float or migrate between the two nodes. The node with current ownership of a cluster IP address is active for that address.

A load balancer also uses a virtual IP as the entry point to a set of servers. These servers tend to be active at the same time. This virtual IP address is not assigned to any individual server but to the load balancer which acts as a proxy between servers and their clients.