Cluster Introduction ?

At the present time, cluster server and workstation systems are mostly used in High Availability applications and in scientific applications such as numerical computations. 

   Clusters can offer

• High performance
• Large capacity
• High availability
• Incremental growth

   Clusters Used for

• Scientific computing
• Making movies
• Commercial servers(web/database/etc)

Requirements
   The main requirements that a clustering algorithm should satisfy are:

• scalability
• dealing with different types of attributes
• discovering clusters with arbitrary shape
• minimal requirements for domain knowledge to determine input parameters
• ability to deal with noise and outliers
• insensitivity to order of input records
• high dimensionality
• interpretability and usability

This article focuses on three types of clusters:

• Fail-over clusters (High Availability)
• Load-balancing clusters
• High-performance clusters

1. Fail-over clusters

The simplest fail-over cluster has two nodes: one stays active and the other stays on stand-by but constantly monitors the active one. In case the active node goes down, the stand-by node takes over, allowing a mission-critical system to continue functioning.

 1a.Red Hat Cluster Suite

 Red Hat Cluster Suite provides two distinct types of cluster:
     * Application/Service Failover - Create n-node server clusters for failover of key applications and services
     * IP Load Balancing - Load balance incoming IP network requests across a farm of servers

With Red Hat Cluster Suite, applications can be deployed in high availability configurations so that they are always operational-bringing "scale-out" capabilities to Enterprise Linux deployments.

 1b. Veritas Cluster Server

VeritasTM Cluster Server from Symantec is a high availability solution for reducing both planned and unplanned downtime. By monitoring the status of applications and automatically moving them to another server in the event of a fault, Cluster Server can dramatically increase the availability of an application or database.

2. Load-balancing clusters

Load-balancing clusters are commonly used for busy Web sites where several nodes host the same site, and each new request for a Web page is dynamically routed to a node with a lower load.

3. High-performance clusters

These clusters are used to run parallel programs for time-intensive computations and are of special interest to the scientific community. They commonly run simulations and other CPU-intensive programs that would take an inordinate amount of time to run on regular hardware.

Monitoring Software

Stuff that will let you keep an eye on your cluster to make sure it's running well.

Big Brother

Big Brother Professional Edition (BBPE) is an easy-to-implement, affordable, web-based solution for IT infrastructure monitoring and diagnostics. Get real-time monitoring for any server (Windows, UNIX, Linux) or device, on any network, from a web browser.

Ganglia

Ganglia is a scalable distributed monitoring system for high-performance computing systems such as clusters and Grids. It is based on a hierarchical design targeted at federations of clusters. It leverages widely used technologies such as XML for data representation, XDR for compact, portable data transport, and RRDtool for data storage and visualization.

Nagios

Nagios is a powerful tool that provides instant awareness of an organization's IT infrastructure and allows the user to detect and repair problems and mitigate future issues before they affect end-users or customers.