If you want to change the root path of a domain in the Nginx web server based on a cookie then you can put the following lines of code in the sites conf file, ie the file within sites-available folder in /etc/nginx/ directory.

 map $http_cookie $rootpath {
	"~*revert_in"  "/var/www/path to/htdocs";
	default                 "/var/www/original/htdocs";
  }

server {


    server_name test1.loantap.in   www.test1.loantap.in;
    ...
    ...
    ...	
    root $rootpath;
    ...
    ...
    ...
}

The MAP directives allow us to set the $rootpath variable based on conditions specified below. This $rootpath is then used to set the path in server directive.

This technique allows us to test files level changes on a production website with an existing database.