Redis sentinel vs clustering

Question

I understand redis sentinel is a way of configuring HA (high availability) among multiple redis instances. As I see, there is one redis instance actively serving the client requ

Answer 1

Redis can operate in partitioned cluster (with many masters and slaves of those masters) or a single instance mode (single master with replica slaves).
The link here says:

When using Redis in single instance mode, in which a single Redis server manages the entire unpartitioned database, Redis Sentinel is used to manage its availability

It also says:

A Redis cluster, in which data is partitioned among multiple primary instances, manages availability by itself and requires no extra components.

So HA can be ensured in the 2 mentioned scenarios. Hope this clears the doubts. Redis cluster and sentinels are not alternative to each other. They are just used to ensure HA in different cases of partitioned or non-partitioned master.