hi, is there a way to use nginx to publish the maintenance file

[Space Lee]

I have a question, if I want to use nginx to main the maintenance file, and what's the easiest way for me to change a web to maintained status when it's in emergency? 

another question, as you see, that twitter always has Over Capacity Page, and how to implement this? is there any need to nginx to read something and then redirect all the connection to over capacity page?