Luckily when a client demands something outrageous they tend to discover that it comes with a formidable price tag. Uptime requires redundancy, redundancy requires a substantial increase in cost without even factoring in the additional development time.<p>A theoretical (as you can't guarantee it anyway) 100% uptime requires a ridiculous amount of redundancy (i.e. consider that you now need to factor in every idiot with a backhoe[1], car[2] or boat[3]). At 100% uptime you have to consider not just your site being up but all the infrastructure between your servers and the given user being up as well.<p>What's better is discussing with your client what happens when they hit downtime and how the negative impact can be mitigated. Can you run a limited service that covers the core functionality of the website (i.e. only make the core components redundant[4])? What parts of the service are absolutely desired? How much money will the client lose (either directly or through lost customer faith)?<p>You'll tend to find the client will realise the time is better spent developing features or improving the user experience than worrying over that last 0.1% between 99.9 and 100.<p>[1]: <a href="http://www.wired.com/science/discoveries/news/2006/01/70040" rel="nofollow">http://www.wired.com/science/discoveries/news/2006/01/70040</a><p>[2]: <a href="http://www.datacenterknowledge.com/archives/2010/05/13/car-crash-triggers-amazon-power-outage/" rel="nofollow">http://www.datacenterknowledge.com/archives/2010/05/13/car-c...</a><p>[3]: <a href="http://en.wikipedia.org/wiki/2008_submarine_cable_disruption" rel="nofollow">http://en.wikipedia.org/wiki/2008_submarine_cable_disruption</a><p>[3]: <a href="http://techblog.netflix.com/2011/07/netflix-simian-army.html" rel="nofollow">http://techblog.netflix.com/2011/07/netflix-simian-army.html</a>
To some extend, 100% uptime is like perfect security. There is no perfect security, the closer you get to it, the more expensive it is. At some point, you have to draw a line and design your system to deal with the downtime.
I believe every client would like to have a system with a 100% up time. You should instead frame the question to what eplison error is acceptable which in you case, is 0.02% error.
It says in the article that "In 2007, only 3 of the top 20 websites were able to achieve 5 nines or 99.999% uptime." Among the top 3 was Myspace. Which is funny because you need traffic to worry about Uptimes...