"Zero Downtime" is easy to say but very hard to achieve. Even sites as large as Yahoo! and eBay periodically go down due to technical problems. There is a big difference between your site going down due to outside "hack" or DOS (Denial of Service) attacks, and your site going down due to poor planning, bad design, inadequate code or a technical staff lacking in experience. There is no 100% solution to down time. Those thinking they are completely safe from outside attack are most certainly vulnerable. Hackers everyday find new exploits and loopholes in servers. In addition, it is virtually impossible to stop a college student from setting up 1,500 servers on ultra high-speed connections to bombard your website with traffic causing a Denial of Service to all your paying customers (just ask Microsoft). You can however prevent 100% of the downtime resulting from bad code or poor system design.