How do you implement Redis high availability with automatic failover?

Redis high availability ensures continuous service through automatic failover, eliminating single points of failure and maintaining data consistency.\n\n• **Why High Availability Matters:**\nMinimizes downtime, ensures business continuity, maintains user experience, protects against hardware failures, and supports SLA requirements.\n\n• **Redis Sentinel Architecture:**\nMonitors master and replicas, detects failures automatically, performs failover elections, and provides service discovery for clients.\n\nMinimum 3 Sentinels for quorum\nAutomatic master promotion\nClient notification of topology changes\n\n• **Sentinel Configuration:**\nport 26379\nsentinel monitor mymaster 192.168.1.100 6379 2\nsentinel down-after-milliseconds mymaster 5000\nsentinel failover-timeout mymaster 10000\n\n• **Master-Replica Setup:**\n# Master\nrequirepass strongpassword\n\n# Replica\nreplicaof 192.168.1.100 6379\nmasterauth strongpassword\nreplica-read-only yes\n\n• **Client-Side Failover:**\nfrom redis.sentinel import Sentinel\n\nsentinel = Sentinel([("host1", 26379), ("host2", 26379)])\nmaster = sentinel.master_for("mymaster", password="pass")\nreplica = sentinel.slave_for("mymaster", password="pass")\n\n# Automatic failover handling\nmaster.set("key", "value") # Writes to current master\nvalue = replica.get("key") # Reads from replica\n\n• **Failover Process:**\nSentinels detect master failure, reach quorum agreement, elect new master, reconfigure replicas, and notify clients.\n\n• **Monitoring and Alerting:**\nTrack failover events, monitor replication lag, alert on topology changes, and validate data consistency.\n\n• **Best Practices:**\nDeploy Sentinels on separate servers, use odd numbers (3, 5, 7), test failover scenarios regularly, implement proper client retry logic, and document recovery procedures.