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Glossary
This Glossary contains definitions of terms used in the HACMP for Linux: Installation and Administration Guide. The definitions assume a general familiarity with terminology for HACMPTM and on Linux.
Also see the HACMP Master Glossary.
A
application
A service, such as a database, or a collection of system services and their dependent resources, such as a service IP label associated with your application, or an application server, that you want to keep highly available with the use of HACMP.
application server
A collection of an application start and stop scripts that you provide to HACMP, by entering the pathnames for the scripts in the WebSMIT user interface. An application server is “a resource” associated with an application, you include it in a resource group and HACMP ensures its high availability (the fact that the application can start and stop successfully no matter on which cluster node it is currently running).
C
cluster IP network
A cluster IP network is used for cluster communications between the nodes and for sending heartbeating information. All IP labels configured on the same HACMP network share the netmask, but may be required to have different subnets. You also must add the IP addresses for an IP cluster network to the /etc/hosts file on each node.
cluster node
A physical machine, typically an AIX 5L or a Linux server on which you install HACMP. A cluster node also hosts an application. A cluster node serves as a server for application’s clients. HACMP’s role is to ensure continuous access to the application, no matter on which node in the cluster it is currently active.
See also home node and takeover node.
cluster resources
Resources that include volume groups, an application server, and a service IP label. All or some of these resources can be associated with an application you plan to keep highly available. You include cluster resources into resource groups.
cluster startup
The starting of HACMP cluster services on the node(s).
cluster shutdown
The stopping of HACMP cluster services on the node(s).
F
fallback
An action of a resource group, when HACMP returns it from a takeover node back to the home node. You choose a fallback resource group policy from a predefined list in WebSMIT.
See also resource group startup and fallover.
fallover
An action of a resource group, when HACMP moves it from one node to another. In other words, a resource group and its associated application fall over to another node. You choose a resource group fallover policy from a predefined list in WebSMIT.
See also resource group startup, and fallback.
H
heartbeat
State-of-health message exchanged between network modules. HACMP uses these to track the membership and status of the cluster nodes. A means of detecting failure in the cluster.
home node
A node on which the application is hosted based on your default configuration, and under normal conditions.
I
IP label
A name of a network interface card (NIC) that you provide to HACMP. Network configuration for HACMP requires planning for several types of IP labels:
base (or boot) IP labels service IP labels (the ones through which a connection for a highly available application is established) (optional) backup IP labels. IP aliases for HACMP network configuration. Node-bound persistent IP labels on each node. To ensure high availability and access to the application, HACMP “moves” the service IP label/address associated with the application to another node in the cluster, using the function called IPAT via IP Aliasing.
See also IP Address Takeover via IP Aliasing (IPAT via IP Aliasing).
IP alias
An alias placed on an IP label. It coexists on an interface along with the IP label. Networks that support Gratuitous ARP cache updates enable configuration of IP aliases.
See also IP Address Takeover via IP Aliasing (IPAT via IP Aliasing).
IP Address Takeover (IPAT)
A process whereby a service IP label on one node is taken over (or moved) to a backup node in the cluster. HACMP uses IPAT to provide high availability of IP service labels that belong to resource groups (and provide access to applications).
HACMP for Linux supports IPAT via IP Aliasing.
IP Address Takeover via IP Aliasing
A default method of IPAT used in HACMP for AIX 5L and also the only method of IPAT used in HACMP for Linux.
HACMP uses IPAT via IP Aliasing in cases when it must automatically recover a service IP label on another node. To configure IPAT via IP Aliasing, you configure service IP labels and their aliases to the system. When HACMP performs IPAT during automatic cluster events, it places an IP alias (recovered from the “failed” node) on top of the service IP address on the takeover node. Access to the application is preserved.
P
partitioned cluster
Complete loss of communication between nodes in the cluster. Occurs when all TCP/IP-based networks connecting cluster nodes fail, if a global cluster network is not defined. One or more nodes are completely isolated from the other nodes.
pre- and post-events
Customized scripts provided by you (or other system administrators), that you can make known to HACMP and that will be run prior a particular cluster event, or after a particular cluster event.
For more information on pre- and post-event scripts, see the chapter on Planning Cluster Events in the HACMP for AIX 5L Planning Guide.
R
resource group
A collection of cluster resources. Cluster resources can include volume groups, an application server, and a service IP label. All or some of these resources can be associated with an application you plan to keep highly available.
See also cluster resources.
resource group startup
An activation of a resource group and its associated resources on a specified cluster node. You choose a resource group startup policy from a predefined list in WebSMIT.
resource group fallback
See fallback.
resource group fallover
See fallover.
resource group takeover
See takeover.
RSCT (Reliable Scalable Cluster Technology)
IBM RSCT services provide scalability, notify distributed subsystems of software failure, and coordinate recovery and synchronization among all subsystems in the software stack. This package of services is a prerequisite for HACMP for Linux.
S
startup
see cluster startup.
selective fallover
An automatically launched function of HACMP that attempts to selectively move only a resource group that has been affected by an individual resource failure to another node in the cluster, rather than moving all resource groups.
shutdown
See cluster shutdown.
synchronization
An HACMP function during which the system ensures that the user-configured information is synchronized across all currently active nodes in the cluster.
T
takeover
An action during which HACMP takes over resources from one node and moves them to another node. A backup node is referred to as a takeover node.
takeover node
A backup cluster node on which HACMP may move the application, either on your request (for instance, if you want to perform planned maintenance on the home node), or automatically, due to a cluster component failure. In HACMP for Linux v.5.4, a cluster configuration includes up to eight nodes, therefore, you can have more than one takeover node for a particular application.
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