Automatic trigger to backup

Hi. Is there any possibility for creating trigger file automatically in
postgres. Scenario is as follows :

There are some application which is having this postgres database. There are
main & backup database. Application is normally connected to first server.
If main server fails, application should connect to backup server. This is
PITR environment where WAL files are transferring from the main to backup.

Manually we are creating the trigger file for that application to connect to
backup database which will be master. Then we need to make previous master
as slave.

I need to know the automatic creation of trigger file....?

Vinay