A high-volume site like Yahoo! knows that the actual quality of service any web server provides to end users basically depends on network-transfer speed and server response time. Network-transfer speed refers to the Internet-link bandwidth while server-response time depends upon resources including fast CPU, lots of RAM and good I/O performance. Once these resources are exhausted and the web-server is encountering heavy traffic, a problem would surely arise.
Load Balancing
A problematic situation pertaining to difficulty in handling high volumes of incoming traffic can be solved either through installing more RAM on existing machines or replacing the CPU with a faster one. The use of faster or dedicated SCSI controllers and disks with shorter access time can also be done. Software can be tuned so that the operating system parameters and web server software can be adjusted to achieve better performance.
An alternative approach is to improve performance by increasing the number of web servers. This approach would attempt to distribute traffic unto a cluster of back-end web servers that need not be large-scale machines. Web server scalability is achieved when...