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How does Redis Cluster automatically handle failover when a master node becomes unavailable? What are the key limitations of Redis Cluster that developers should be aware of compared to a single instance Redis setup? How do you monitor the overall health and status of a Redis Cluster to catch problems before they affect your application? How would you design a Redis Cluster deployment to properly balance high availability, performance, and cost for a large scale production application?
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What is a split brain scenario in the context of Redis Cluster, and how does the cluster protect against it?

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Answer

A split brain scenario happens when a network partition causes part of the cluster to lose contact with the rest, potentially leading to two different nodes both believing they are the legitimate master for the same hash slots, and Redis Cluster protects against this by requiring a majority of master nodes to agree before promoting a replica, refusing to serve writes on a minority side of the partition.
-- A cluster requires a majority of masters to be reachable
-- to accept new writes, protecting data consistency
redis-cli cluster info
Real-world example A cluster experiencing a temporary network split between two data centers automatically stops accepting writes on the minority side, preventing conflicting data changes from happening independently on both sides of the partition.

Common follow-ups: What happens to write requests sent to the minority side during a network partition?;How do you configure the cluster's behavior for handling this kind of partition?

Redis Sentinel & High Availability;Redis Backup & Disaster Recovery
All 7 Clustering questions