Installation guide

3.3 Network Requirements

There should be at least two Network Interface Cards (NIC), whether embedded or added to

each server. Where multiple network interfaces are available, NIC bonding can be

implemented for additional availability and is the only current method providing a NIC failover

ability. One bonded interface will be configured with an external IP address while the other will

be configured as an interconnect between cluster members using local network connectivity.

Clusters are very dependent on constant communication between nodes which are

maintained across the local interconnect. It is highly recommended that a private network be

used for all intra-cluster communication.

The Red Hat cluster infrastructure in Red Hat Enterprise Linux 5 uses multicast. Some

network switches require special configuration settings for a well functioning multicast

operation. Please refer to the hardware vendor's configuration guide for correct multicast

configurations.

4 Red Hat Cluster Basics

4.1 OpenAIS

In Red Hat Enterprise Linux 5, the core cluster infrastructure is based on the OpenAIS

framework. OpenAIS is an open source implementation of the Application Interface

Specification defined by the Service Availability Forum, based upon extended virtual

synchrony. The project currently implements Application Programming Interfaces (API) for

application failover, application defined checkpointing, application eventing, extended virtual

synchrony, and cluster membership.

Today, OpenAIS is the state of the art, core cluster framework included in most Enterprise

Linux distributions.

The heart of OpenAIS is the aisexec daemon, into which various services are loaded.

OpenAIS uses multicast for the internal cluster communication.

4.2 CMAN

Cluster Manager (CMAN) is a Red Hat specific service module that loads in the OpenAIS

daemon. It provides a user API that is used by Red Hat layered cluster components.

CMAN also provides additional functionality such as APIs for a quorum disk, the quorum

itself, conditional shutdown, and barriers.

4.3 Quorum

A cluster typically uses shared data resources such as a cluster file system (e.g., GFS) or

local file systems controlled by the cluster resource management system (e.g., rgmanager).

The cluster must be aware of the current state of the shared resources at all times. Therefore,

it must be guaranteed that every critical transition within the cluster cannot compromise data

integrity.