redis-sentinel
High availability monitoring for Redis clusters
TLDR
Start Sentinel
SYNOPSIS
redis-sentinel configfile_
DESCRIPTION
Redis Sentinel provides high availability for Redis deployments through continuous monitoring, automatic failover, and notification. It watches master and replica instances, and when a master becomes unreachable and a quorum of Sentinel processes agrees it is down, it automatically promotes a replica to master and reconfigures the remaining replicas to use the new master.
Sentinel also acts as a configuration provider, allowing clients to discover the current master address for a named service. Multiple Sentinel instances (at least three recommended) form a distributed system that reaches consensus on failover decisions, preventing split-brain scenarios.
EXAMPLES
redis-sentinel /etc/redis/sentinel.conf
# Or via redis-server
redis-server sentinel.conf --sentinel
# Query masters
redis-cli -p 26379 sentinel masters
# Get master address
redis-cli -p 26379 sentinel get-master-addr-by-name mymaster
# List replicas
redis-cli -p 26379 sentinel replicas mymaster
# Failover manually
redis-cli -p 26379 sentinel failover mymaster
CONFIGURATION
/etc/redis/sentinel.conf
Main Sentinel configuration file defining monitored masters, quorum thresholds, and failover parameters.sentinel monitor name host port quorum
Define a master to monitor with the minimum number of Sentinels that must agree it is down before failover.sentinel down-after-milliseconds name ms
Time in milliseconds a master must be unreachable before being considered down.sentinel failover-timeout name ms
Maximum time for a failover operation to complete before being considered failed.
QUORUM
The number after master definition is quorum - minimum Sentinels agreeing master is down before failover.
CAVEATS
Need at least 3 Sentinels for robustness. Port 26379 default. Modifies config file on failover.
HISTORY
Redis Sentinel was introduced in Redis 2.8 by Salvatore Sanfilippo for Redis high availability.
SEE ALSO
redis-server(1), redis-cli(1)