How to run redis sentinel monitoring redis servers

Question

I have 3 redis servers running with 3 sentinels on each host
3 redis-3 sentinels(total 3 hosts)

1. Can I run sentinel on a separate host or it should always run along with redis-server?
   3 redis on 3 hosts 3 sentinels on 3 other hosts(total 6 hosts)
2. Is it possible to monitor all the 3 redis servers with only one redis sentinel?
   3 redis on 3 host 1 sentinel on 1 host(total 3 or 4 hosts)

Answer 1

1. You can run sentinel on a separate hosts or on the same hosts. The benefit of running it in separate hosts is that the sentinel instances will not be affected by load on the Redis instances. The benefit of running it on the same hosts is mainly cost.
2. It might be possible but doesn't make any sense. The benefit of Redis sentinel deployment over Redis single node deployment is that it adds high availability (HA). It means that in case of master failure one of the slaves will be promoted to master and the cluster will continue to function. If you have only single sentinel instance, you don't have HA since failure in sentinel instance will cause the cluster to fail. Therefore to achieve HA you must have at least 3 sentinel instances running on different physical nodes. If you don't need HA, just run Redis single instance without sentinel.