Causes of Failure in Web Applications (CMU-PDL-05-109)

This report investigates the causes and prevalence of failure in Web applications. Data was collected by surveying case studies of system failures and by examining incidents of website outages listed on technology websites such as CNET.com and eweek.com. These studies suggest that software failures and human error account for about 80% of failures. The report also contains an appendix that serves as a quick reference for common failures observed in Web applications. This appendix lists over 40 incidents of real-world site outages, outlining how these failures were detected, the estimated downtime, and the subsequent recovery action.