[seiji]

You shouldn't need haproxy in the loop at all.

If your redis client is Sentinel-aware, you ask your client directly "give me the redis master server" and it asks Sentinel which server is master. The only ip address involved for your configuration is the address of the sentinel(s).

haproxy will take 30 seconds to detect your failure. Sentiel will notify you immediately. Sentinel is the one determining the exact state of the master election, and it'll be very chatty when a new master replaces the old one.