How can i switch to slave database in case of master fail?

I have 2 MySQL instances. One is master and the second is a slave. I want to configure the rails app in a way that if the connection to my master database failed, then auto-connect to the slave database and slave will become master. In this way, the site will never go offline due to the MySQL server crash.
But I am not able to find any solution in rails with mysql2 adapter to do so. Can anyone help me with this?