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What is Redis Sentinel, and what role does it play in providing high availability for a non clustered Redis setup?

Beginner

Answer

Redis Sentinel is a separate monitoring system that continuously watches your primary and replica Redis instances, and if it detects the primary has failed, it automatically coordinates promoting one of the replicas to become the new primary, providing automatic failover without needing to run a full Redis Cluster.
-- Sentinel configuration file
sentinel monitor mymaster 192.168.1.10 6379 2
Real-world example A company running a simple primary and replica Redis setup adds Sentinel to automatically detect and recover from a primary failure, without needing the added complexity of setting up a full Redis Cluster.

Common follow-ups: How many Sentinel instances are recommended for a production deployment?;What is the difference between using Sentinel and using Redis Cluster for high availability?