Run a live mirror of a wordpress site

Hi, I’m trying to find a way of running an identical mirror, duplicate, cloned, exactly similar version of wordpress alongside my live site. In my head the two sites start by being cloned and then when content is changed on one site it copies it to the other. I would like to have an identical copy to the live site so I can test plugins and output feeds from a different location to my main site.

What would be ideal would be a plugin that will duplicate the activity of one wordpress install to another so they are always the same.

Thanks!