tomcat - Webapp Hostname - Autoswitch to DR server when primary server went down -

my title may not make sense, here explanation of question.

i have web application url - https://generic.abc.com:8080/myapp/ , webserver tomcat 7.

now, application hosted in server 'myserver1'. url https://myserver1:8080/myapp/ work.

also, dr server on 'mydrserver1', hence if primary host down , dr host up, application runs url - https://mydrserver1:8080/myapp/

again, in situation if load generic url, automatically loads dr app.

my question is, how generic host connected pr , dr host? concept here?

thanks.