A server cluster is a group of independent servers that are managed as a single system for higher availability, easier manageability, and greater scalability.
In a Web server environment, server clusters can be defined in two basic ways:
In a Web server environment, server clusters can be defined in two basic ways:
Active/Active
- There are multiple independent, redundant servers
- The load is distributed through round-robin DNS
- The load is balanced by a load-balancing solution
- Multiple servers are configured to provide a service
- Only a single server provides the service at any given time
- Other servers serve as hot-spares in case of a server (service) problem or a site hosted on the servers suddenly start getting load spikes such as when being slashdotted.
Now a days, many shared web hosting providers are turning to a web server cluster solution over managing individual web servers on independent machines. Clustering is said to provide some respite to the performance issues.
Eli M. Dow and Frank LeFevre, both, Software Engineers at IBM have written this insightful albeit rather technical article which explains how to setup an Apache web server cluster in 5 easy steps.
From the article ...
Spreading a workload across multiple processors, coupled with various software recovery techniques, provides a highly available environment and enhances overall RAS (Reliability, Availability, and Serviceability) of the environment. Benefits include faster recovery from unplanned outages, as well as minimal effects of planned outages on the end user.To get the most out of this article, you should be familiar with Linux and basic networking, and you should have Apache servers already configured. Our examples are based on standard SUSE Linux Enterprise Server 10 (SLES10) installations, but savvy users of other distributions should be able to adapt the methods shown here.
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