Redis Sentinel is a dedicated process to automate and simplify the Redis replication failover and switchover.
In this article, we will start with 3 Nodes. We will have two Redis instances on two different nodes – 1 master and 1 replica (or slave). Sentinel will be co-located on those 2 nodes, plus an additional node on one of our web servers.
Normally you would co-locate a Redis instance on the web/application server and access it via localhost or through a UNIX socket file. This is the straightforward way to incorporate Redis into the application.