I searched around and I was surprised that I couldn't find an answer to this question. My assumption is that you have multiple servers. Normally they both will be doing their specific take (for the rest of this I will assume a simple website). Now lets say server A & B need updates. Do you update server A while server B keeps pushing out the webpage and then when server A is okay you update server B? This seems like it would work in small scale but seems horrible in large scale due to the fact that you'd need twice the power that you normally have. When dealing with a large number of servers do you update small sections at a time? I thought the problem with this would be if server A can't work alongside server B C D E or F any-longer that's not that bad. But when you start updating you slowly lose this small percentage.

What is the proper way to deal with updates like this?