If there is only one web server responding to all the incoming HTTP requests for your website, the capacity of the web server may not be able to handle high volumes of incoming traffic once the website becomes popular. The website's pages will load slowly as some of the users will have to wait until the web server is free to process their requests. The increase in traffic and connections to your website can lead to a point where upgrading the server hardware will no longer be cost effective.

In order to achieve web server scalability, more servers need to be added to distribute the load among the group of servers, which is also known as a server cluster. The load distribution among these servers is known as load balancing. Load balancing applies to all types of servers (application server, database server), however, we will be devoting this section for load balancing of web servers (HTTP server) only.

About load balancing mechanism - IP Spraying

When multiple web servers are present in a server group, the HTTP traffic needs to be evenly distributed among the servers. In the process, these servers must appear as one web server to the web client, for example an internet browser. The load balancing mechanism used for spreading HTTP requests is known as IP Spraying. The equipment used for IP spraying is also called the 'load dispatcher' or 'network dispatcher' or simply, the 'load balancer'. In this case, the IP sprayer intercepts each HTTP request, and redirects them to a server in the server cluster. Depending on the type of sprayer involved, the architecture can provide scalability, load balancing and failover requirements.