How to fix +elected-leader: Won election for epoch in Redis

# Connect to any Sentinel instance
redis-cli -p 26379

# Check master status and current epoch
SENTINEL master <master-name>

# Look for relevant fields:
# - config-epoch: Current configuration version
# - leader-epoch: Epoch of the current/last failover leader
# - failover-state: Current failover stage

# View recent Sentinel events
SENTINEL events <master-name>

# Watch Sentinel logs in real-time
tail -f /var/log/redis/sentinel.log

# Expected sequence after +elected-leader:
# +elected-leader: Won election for epoch <N>
# +selected-slave: <replica-ip>:<port>
# +promoted-slave: <replica-ip>:<port>
# +reconf-slaves: <master-name>
# +failover-end: Failover finished successfully

# Verify new master address
SENTINEL get-master-addr-by-name <master-name>

# Confirm all Sentinels agree on new master
SENTINEL sentinels <master-name> | grep -i ip

# Check quorum requirements
SENTINEL master <master-name> | grep quorum

# View Sentinel configuration
grep -E "quorum|down-after-milliseconds|failover-timeout" /etc/redis/sentinel.conf

# Example configuration for 3-Sentinel setup:
sentinel monitor mymaster 127.0.0.1 6379 2  # quorum=2 (majority of 3)
sentinel down-after-milliseconds mymaster 5000
sentinel parallel-syncs mymaster 1
sentinel failover-timeout mymaster 180000

# Test connectivity to new master
redis-cli -h <new-master-ip> -p 6379 PING

# Check replication status on new master
redis-cli -h <new-master-ip> -p 6379 INFO replication

# Expected output:
# role:master
# connected_slaves:2  (or however many replicas you have)

# In your application, use Sentinel-aware clients:
# Node.js (ioredis):
const Redis = require('ioredis');
const redis = new Redis({
  sentinels: [
    { host: 'sentinel1', port: 26379 },
    { host: 'sentinel2', port: 26379 },
    { host: 'sentinel3', port: 26379 },
  ],
  name: 'mymaster',
});

# Parse Sentinel logs for election events
grep -E "\+elected-leader|\+failover-end|\-failover-abort" /var/log/redis/sentinel.log

# Count elections over time (frequent elections indicate instability)
grep "+elected-leader" /var/log/redis/sentinel.log | wc -l

# Example monitoring with Prometheus/Grafana:
# - Alert on multiple elections within short timeframes
# - Track time from +elected-leader to +failover-end
# - Monitor epoch progression for anomalies

# Log aggregation query (e.g., in ELK Stack):
# message:"elected-leader" AND message:"Won election for epoch"
# | stats count by sentinel_host, epoch