Redis Monitoring Guide: Key Metrics, Alerts & Tools (2026)

# Get all stats
redis-cli INFO

# Memory section only
redis-cli INFO memory

# Stats section (hits, misses, evictions, connections)
redis-cli INFO stats

# Replication section
redis-cli INFO replication

# Keyspace section (key counts per DB)
redis-cli INFO keyspace

# Example memory output:
# used_memory:1234567890
# used_memory_human:1.15G
# used_memory_rss:1456789012
# mem_fragmentation_ratio:1.18
# maxmemory:2147483648
# maxmemory_human:2.00G
# maxmemory_policy:allkeys-lru

# Docker Compose example
version: '3'
services:
  redis-exporter:
    image: oliver006/redis_exporter:v1.62
    environment:
      REDIS_ADDR: "redis://redis:6379"
      REDIS_PASSWORD: "$REDIS_PASSWORD"
    ports:
      - "9121:9121"
    depends_on:
      - redis

# Prometheus scrape config
scrape_configs:
  - job_name: 'redis'
    static_configs:
      - targets: ['localhost:9121']
    scrape_interval: 15s

# Key metrics exposed:
# redis_memory_used_bytes
# redis_memory_max_bytes
# redis_keyspace_hits_total
# redis_keyspace_misses_total
# redis_evicted_keys_total
# redis_connected_clients
# redis_blocked_clients
# redis_replication_lag
# redis_up (1 = healthy)

groups:
  - name: redis
    rules:
      # Redis is down
      - alert: RedisDown
        expr: redis_up == 0
        for: 1m
        labels:
          severity: critical
        annotations:
          summary: "Redis instance is not responding"

      # Memory pressure
      - alert: RedisMemoryHigh
        expr: |
          redis_memory_used_bytes / redis_memory_max_bytes > 0.8
        for: 5m
        labels:
          severity: warning
        annotations:
          summary: "Redis memory usage above 80%"

      # Evictions happening (cache too small)
      - alert: RedisEvictions
        expr: rate(redis_evicted_keys_total[5m]) > 0
        for: 5m
        labels:
          severity: warning
        annotations:
          summary: "Redis is evicting keys — cache may be undersized"

      # Cache hit ratio below 90%
      - alert: RedisLowHitRate
        expr: |
          rate(redis_keyspace_hits_total[5m]) /
          (rate(redis_keyspace_hits_total[5m]) + rate(redis_keyspace_misses_total[5m])) < 0.9
        for: 10m
        labels:
          severity: warning
        annotations:
          summary: "Redis cache hit rate below 90%"

      # Connection limit approaching
      - alert: RedisTooManyConnections
        expr: redis_connected_clients > (redis_config_maxclients * 0.9)
        for: 5m
        labels:
          severity: warning
        annotations:
          summary: "Redis approaching max client connections"

      # Replication lag
      - alert: RedisReplicationLag
        expr: redis_replication_lag > 1048576  # 1MB
        for: 5m
        labels:
          severity: warning
        annotations:
          summary: "Redis replica is lagging behind primary"

# Configure slow log (10ms threshold, keep 128 entries)
redis-cli CONFIG SET slowlog-log-slower-than 10000
redis-cli CONFIG SET slowlog-max-len 128

# View the 25 most recent slow commands
redis-cli SLOWLOG GET 25

# Output format:
# 1) 1) (integer) 14          # Entry ID
#    2) (integer) 1714500000  # Unix timestamp
#    3) (integer) 28000       # Execution time in microseconds (28ms)
#    4) 1) "KEYS"             # Command + arguments
#       2) "*"
#    5) "127.0.0.1:42321"
#    6) ""

# Reset the slow log
redis-cli SLOWLOG RESET

# Check replication status on the primary
redis-cli INFO replication

# Key output fields:
# role: master
# connected_slaves: 2
# slave0: ip=10.0.1.5,port=6379,state=online,offset=1234567,lag=0
# slave1: ip=10.0.1.6,port=6379,state=online,offset=1234500,lag=0
# master_repl_offset: 1234570
# repl_backlog_size: 1048576

# Lag calculation:
# slave lag = master_repl_offset - slave_offset
# slave0 lag = 1234570 - 1234567 = 3 bytes (healthy)
# slave1 lag = 1234570 - 1234500 = 70 bytes (tiny, normal)

# Check on a replica
redis-cli -h replica-host INFO replication
# role: slave
# master_host: 10.0.1.4
# master_link_status: up   # Should be "up"
# master_sync_in_progress: 0  # 1 = full resync in progress (expensive)