There are two things that cause sites to go down:
Something breaks.
Too much traffic.
When things break, there’s nothing to do but failover, examine, and fix.
But when there’s too much traffic, you’re screwed. The reason you’re getting so much traffic is because you’ve done something to earn it. Your site has made it on to Digg or Reddit or even TV. Failing over to a status page is admitting that you haven’t done your job. Staying up means that some people will see the site, maybe, but after a stupidly long wait. And then you become ‘that site’ that was taken down by too much traffic.
So as a web architect, this is your absolute worst moment. Everything you’ve done over the past months or years is falling down miserably in front of you, and there isn’t anything you can do at that moment that will make a meaningful difference. Unless, of course, your architecture is set up so you can increase capacity by just turning up more servers. Among software architects, this is know as being able to scale horizontally
So when the site is being built, it’s extremely important that every choice you make supports scaling horizontally, with each layer able to be spread across many servers. Storage, session handling, database, apache […] are all different layers. They all need to be able to handle more capacity just by adding additional services to whatever layer needs it.
Having the horizontal scalable quality is really difficult when trying to get a site out quickly. architecture is something that will often get de- prioritized because there is no immediate result. However, taking the extra time to build an application that follows the horizontally scalable patterns is extremely important. Without spending that extra time, you can easily be wiped out by the [Digg effect](http://www.ndesign-studio.com/blog/updates/the- digg-effect/).
The biggest takeaway is when thinking about how to build your application, focus on making it scale horizontally. So when the moment comes when you get on Digg, you can spin up some more servers, sit back, and have a drink.