Use Something Webscale
There really is only one choice if you want to go webscale and never have any down time. HTML. HTML does all the things. This is all in pure HTML and look at how fast this page loads! Stackoverflow aint got a thing on these load times.
Github spends more time down than up. That's because ruby. When you have to name a language after something pretty to get people to use it then you know it is crap.
Node... nuff said.
Use PHP for webscales when you need a dynamic language. It is used by facebook which never goes down and has no bugs at all! So many people use it for a reason, it is the best web application on the net to date.