redis

# Redis Configure, operate, and optimize Redis for caching, queues, rate limiting, and real-time data storage. ## When to Use - You need a low-latency in-memory cache to reduce database load. - Your application requires rate limiting, session storage, or leaderboards. - You need pub/sub messaging between services. - You want a distributed lock or job queue backed by an in-memory store. ## Prerequisites - Linux server or Docker. - Root or sudo access for package installation. - Redis 7.x recommended for production. ## Installation and Setup ```bash # Debian / Ubuntu sudo apt update sudo apt install -y redis-server # RHEL / Amazon Linux sudo dnf install -y redis # Start and enable sudo systemctl enable --now redis-server # Verify redis-cli ping # Expected output: PONG ``` ## Core Configuration Edit `/etc/redis/redis.conf`: ```ini # Network bind 0.0.0.0 port 6379 protected-mode yes requirepass strong_redis_password # Memory maxmemory 2gb maxmemory-policy allkeys-lru # Connections maxclients 10000 timeout 300 tcp-keepalive 60 # Logging loglevel notice logfile /var/log/redis/redis-server.log # Security — disable dangerous commands in production rename-command FLUSHALL "" rename-command FLUSHDB "" rename-command CONFIG "" rename-command DEBUG "" ``` ```bash sudo systemctl restart redis-server ``` ## redis-cli Commands Reference ```bash # Connect with authentication redis-cli -a strong_redis_password # Connect to a remote host redis-cli -h 10.0.0.5 -p 6379 -a strong_redis_password ``` ### String Operations ``` SET user:1:name "Alice" GET user:1:name # Set with TTL (seconds) SETEX session:abc123 3600 '{"userId":1}' # Set only if key does not exist (distributed lock pattern) SET lock:order:42 "worker-1" NX EX 30 # Increment counters INCR page:views:/home INCRBY api:quota:user:1 -1 ``` ### Hash Operations ``` HSET user:1 name "Alice" email "alice@example.com" plan "pro" HGET user:1 email HGETALL user:1 HINCRBY user:1 login_count 1 ``` ### List Operations (Queues) ``` LPUSH queue:emails '{"to":"alice@example.com","subject":"Welcome"}' RPOP queue:emails LLEN queue:emails # Blocking pop (worker pattern) BRPOP queue:emails 30 ``` ### Set and Sorted Set Operations ``` # Sets — unique tags SADD article:1:tags "redis" "database" "caching" SMEMBERS article:1:tags SISMEMBER article:1:tags "redis" # Sorted sets — leaderboards ZADD leaderboard 1500 "player:1" 2300 "player:2" 1800 "player:3" ZREVRANGE leaderboard 0 9 WITHSCORES ZINCRBY leaderboard 100 "player:1" ZRANK leaderboard "player:2" ``` ### Key Management ``` KEYS user:* # avoid in production — use SCAN instead SCAN 0 MATCH user:* COUNT 100 TTL session:abc123 PERSIST session:abc123 DEL user:old EXPIRE user:1 86400 TYPE user:1 ``` ## Persistence ### RDB Snapshots ```ini # redis.conf — save snapshots at intervals save 900 1 # snapshot if >= 1 key changed in 900 seconds save 300 10 # snapshot if >= 10 keys changed in 300 seconds save 60 10000 # snapshot if >= 10000 keys changed in 60 seconds dbfilename dump.rdb dir /var/lib/redis rdbcompression yes ``` ### AOF (Append-Only File) ```ini appendonly yes appendfilename "appendonly.aof" appendfsync everysec # good balance of safety and performance # Options: always (safest, slowest), everysec (recommended), no (OS decides) # AOF rewrite thresholds auto-aof-rewrite-percentage 100 auto-aof-rewrite-min-size 64mb ``` ### Recommended Production Strategy Use both RDB and AOF together. RDB provides fast restarts and compact backups. AOF provides durability down to 1-second granularity. ```ini save 900 1 save 300 10 appendonly yes appendfsync everysec ``` ## Redis Sentinel (High Availability) Sentinel monitors Redis instances and performs automatic failover. ### Sentinel Configuration ```ini # /etc/redis/sentinel.conf port 26379 sentinel monitor mymaster 10.0.0.1 6379 2 sentinel auth-pass mymaster strong_redis_password sentinel down-after-milliseconds mymaster 5000 sentinel failover-timeout mymaster 60000 sentinel parallel-syncs mymaster 1 ``` Run at least three Sentinel instances for quorum. ```bash # Start Sentinel redis-sentinel /etc/redis/sentinel.conf # Query Sentinel redis-cli -p 26379 SENTINEL masters redis-cli -p 26379 SENTINEL get-master-addr-by-name mymaster redis-cli -p 26379 SENTINEL replicas mymaster ``` ## Redis Cluster Mode Cluster mode distributes data across multiple shards automatically. ```bash # Create a 6-node cluster (3 masters + 3 replicas) redis-cli --cluster create \ 10.0.0.1:6379 10.0.0.2:6379 10.0.0.3:6379 \ 10.0.0.4:6379 10.0.0.5:6379 10.0.0.6:6379 \ --cluster-replicas 1 -a strong_redis_password # Check cluster status redis-cli -c -a strong_redis_password CLUSTER INFO redis-cli -c -a strong_redis_password CLUSTER NODES # Add a new node redis-cli --cluster add-node 10.0.0.7:6379 10.0.0.1:6379 # Rebalance slots redis-cli --cluster rebalance 10.0.0.1:6379 ``` ```ini # redis.conf for cluster nodes cluster-enabled yes cluster-config-file nodes.conf cluster-node-timeout 5000 ``` ## Common Patterns ### Caching with TTL ```bash # Cache a database query result for 5 minutes SET cache:user:42:profile '{"name":"Alice","plan":"pro"}' EX 300 # Cache-aside pattern (pseudocode): # 1. GET cache:key -> if hit, return # 2. Query database # 3. SET cache:key result EX 300 # 4. Return result ``` ### Rate Limiting (Sliding Window) ```bash # Allow 100 requests per minute per user # Using a sorted set with timestamps as scores ZADD ratelimit:user:42 1700000000.123 "req-uuid-1" ZREMRANGEBYSCORE ratelimit:user:42 0 1699999940.000 ZCARD ratelimit:user:42 EXPIRE ratelimit:user:42 60 # If ZCARD >= 100, reject the request ``` ### Pub/Sub Messaging ```bash # Terminal 1 — subscriber redis-cli -a strong_redis_password SUBSCRIBE notifications:order-updates # Terminal 2 — publisher redis-cli -a strong_redis_password PUBLISH notifications:order-updates '{"orderId":42,"status":"shipped"}' # Pattern subscription PSUBSCRIBE notifications:* ``` ### Distributed Locking (Redlock Pattern) ```bash # Acquire lock SET lock:resource:42 "worker-abc" NX EX 30 # Returns OK if acquired, nil if already held # Release lock (use Lua script to ensure atomicity) redis-cli -a strong_redis_password EVAL " if redis.call('get', KEYS[1]) == ARGV[1] then return redis.call('del', KEYS[1]) else return 0 end " 1 lock:resource:42 "worker-abc" ``` ## Docker Compose Setup ```yaml # docker-compose.yml version: "3.9" services: redis: image: redis:7-alpine restart: unless-stopped ports: - "6379:6379" volumes: - redis_data:/data - ./redis.conf:/usr/local/etc/redis/redis.conf:ro command: redis-server /usr/local/etc/redis/redis.conf healthcheck: test: ["CMD", "redis-cli", "-a", "strong_redis_password", "ping"] interval: 10s timeout: 5s retries: 5 redis-sentinel: image: redis:7-alpine restart: unless-stopped ports: - "26379:26379" volumes: - ./sentinel.conf:/usr/local/etc/redis/sentinel.conf command: redis-sentinel /usr/local/etc/redis/sentinel.conf depends_on: redis: condition: service_healthy redis-commander: image: rediscommander/redis-commander:latest restart: unless-stopped ports: - "8081:8081" environment: REDIS_HOSTS: "local:redis:6379:0:strong_redis_password" depends_on: redis: condition: service_healthy volumes: redis_data: ``` ```bash docker compose up -d redis-cli -h 127.0.0.1 -a strong_redis_password ping ``` ## Monitoring ```bash # Real-time stats redis-cli -a strong_redis_password INFO stats redis-cli -a strong_redis_password INFO memory redis-cli -a strong_redis_password INFO replication # Key metrics to watch redis-cli -a strong_redis_password INFO stats | grep -E "keyspace_hits|keyspace_misses" # Hit ratio = hits / (hits + misses) — aim for > 95% # Memory usage breakdown redis-cli -a strong_redis_password MEMORY STATS # Slow log (queries > 10ms by default) redis-cli -a strong_redis_password SLOWLOG GET 10 redis-cli -a strong_redis_password SLOWLOG LEN # Monitor all commands in real time (debugging only — impacts performance) redis-cli -a strong_redis_password MONITOR # Connected clients redis-cli -a strong_redis_password CLIENT LIST ``` ## Troubleshooting | Symptom | Likely Cause | Fix | |---|---|---| | `OOM command not allowed` | `maxmemory` limit reached | Increase `maxmemory` or set a stricter eviction policy | | High latency spikes | RDB save or AOF rewrite forking | Use `save ""` to disable RDB if AOF is enabled; tune `auto-aof-rewrite-min-size` | | `LOADING Redis is loading the dataset in memory` | Large dataset being restored on startup | Wait for load to complete; consider smaller dataset or faster disk | | Cache hit ratio < 90% | TTLs too short or working set exceeds memory | Increase `maxmemory`; review TTL strategy | | Sentinel not failing over | Fewer than quorum Sentinels reachable | Ensure >= 3 Sentinels are running and network-connected | | `CROSSSLOT` error in cluster | Multi-key command spans slots | Use hash tags `{user:42}:profile` to colocate related keys | ## Related Skills - [postgresql](../postgresql/) - Primary database that Redis caches - [mysql](../mysql/) - Primary database that Redis caches - [mongodb](../mongodb/) - Document database that Redis can front - [database-backups](../database-backups/) - Include RDB files in backup strategy