Cluster Overview

A cluster is a group of Netscape Application Servers (NASs) connected by a reliable network that is configured to handle fault tolerance.

A cluster is a group of Netscape Application Servers that are configured to share and synchronize state and session data. A cluster operates independently of load balancing.

A cluster:

  • Maintains integrity of shared state and session data
  • Allows application code to access session data from distributed sources

Reliable Network

Servers in a cluster should be connected by a reliable network.

  • Servers on a network do not have to participate in a NAS cluster.
  • If NAS applications do not share state and session data they do not need a cluster. The administrator might still want to create a cluster because of the failover capabilities.

NAS can load balance to servers both inside and outside of a cluster.

Unavailable Server

Servers in the NAS cluster communicate with the primary server and can detect if that server becomes unavailable. Thus, depending on the role of that server, another server can be promoted to compensate for the unavailable server. This provides fault tolerance within the cluster and creates a stable application environment.

 Cluster Purpose

The purpose of a NAS cluster is to allow session and state data to be shared among a number of servers.

Shared Session

The NAS cluster defines the roles of each server and ensures that the data is the same for all servers.

Access Data

NAS clustering allows session and state data to be accessible to multiple servers. The NAS load-balancing system can be set up so that an application is available from more than one server. The NAS load-balancing service decides which server is the best choice to handle the request. Clustering ensures that the data can be retrieved from any server and that the data is intact.

Fault Tolerance

Clustering provides a system to handle fault tolerance to ensure that data is not lost if a server fails.

If the designated primary server fails, the Sync Backup immediately and transparently takes over as primary server. Meanwhile, a new Sync Backup is assigned and configured automatically so that there is always a Sync Backup.