I would not consider 120 seconds to be excessive when you're failing over to a new master from the hot slave.

Ouch, isn't automatic failover one of the big selling points of RDS?

From what I see, that failover uses DNS. The endpoint stays same, but it's pointed to new IP address or so...And the app may continue to use the cached IP from DNS query. I have to write a daemon to listen to RDS event and restart our app if it detects a failover event :(