🔴 Redis: From Basics to Real-World Usage¶

Redis (Remote Dictionary Server) is a lightning-fast in-memory data store used as a cache, message broker, and lightweight database.
It stores data as key-value pairs, keeps it in RAM for near-instant access, and can optionally persist it to disk.

It’s often used alongside PostgreSQL: Postgres for durability, Redis for speed.

⚙️ 1. What Redis Actually Does¶

Redis keeps everything in memory but optionally syncs to disk (snapshots or append logs).
It supports complex data types, pub/sub messaging, and atomic operations — all with sub-millisecond latency.

Use Case	Example
Cache	Store frequently accessed DB results.
Session Store	Track logged-in users.
Queue / Stream	Background jobs, real-time feeds.
Rate Limiter	Count requests per user/IP.
Pub/Sub	Event notification between services.

👉 In short: Redis trades persistence for speed, but can be configured for both.

🧱 2. Core Concepts¶

Concept	Description
Key	Identifier for a piece of data (string).
Value	Data stored under a key — can be string, hash, list, set, etc.
TTL	Time-to-live (expiration).
Persistence	Data saved to disk (RDB snapshots or AOF logs).
Pub/Sub	Publisher sends messages to channels; subscribers receive them.
Database index	Redis has logical DBs numbered 0–15 by default.

⚡ 3. Basic Commands (Quick Reference)¶

redis-cli                   # Start CLI
ping                        # → PONG
set key "value"             # store
get key                     # retrieve
del key                     # delete
exists key                  # check if exists
expire key 60               # expire after 60s
keys *                      # list all keys (use with caution)
flushall                    # delete everything
````

---

## 🧩 4. Data Structures and Examples

### Strings

```bash
set greeting "Hello"
get greeting
incr counter
decr counter

Hashes (key → fields)¶

hset user:1 name "Alice" email "alice@example.com"
hgetall user:1
hget user:1 email

Lists (ordered queue)¶

lpush queue job1
rpush queue job2
lrange queue 0 -1
lpop queue

Sets (unique values)¶

sadd users "edgaras" "alice"
smembers users
sismember users "bob"

Sorted Sets (ranking)¶

zadd leaderboard 100 "alice" 95 "bob"
zrevrange leaderboard 0 -1 WITHSCORES

Pub/Sub¶

SUBSCRIBE news
PUBLISH news "Server update complete!"

🧠 5. Persistence Modes¶

Redis can persist data in two main ways:

Mode	Description
RDB (Snapshot)	Saves full dataset at intervals (default). Fast, minimal overhead.
AOF (Append Only File)	Logs every operation — safer but slower.
Hybrid	Combines both for speed + durability.

Example in redis.conf:

save 900 1
save 300 10
save 60 10000
appendonly yes

🧰 6. Running Redis with Docker¶

docker run -d \
  --name redis \
  -p 6379:6379 \
  -v redis_data:/data \
  redis:7

Check connection:

docker exec -it redis redis-cli ping

With password:

docker run -d \
  -p 6379:6379 \
  -e REDIS_PASSWORD=secret \
  redis:7 \
  redis-server --requirepass secret

🧩 7. Docker Compose Example¶

version: "3.9"
services:
  redis:
    image: redis:7
    ports:
      - "6379:6379"
    volumes:
      - redis_data:/data
    command: redis-server --appendonly yes
    healthcheck:
      test: ["CMD", "redis-cli", "ping"]
      interval: 5s
      retries: 5

  backend:
    build: ./backend
    environment:
      REDIS_HOST: redis
      REDIS_PORT: 6379

volumes:
  redis_data:

💾 8. Redis + Application Integration (Spring Boot Example)¶

application.properties:

spring.data.redis.host=redis
spring.data.redis.port=6379
spring.data.redis.password=secret

Simple cache usage with Spring:

@Cacheable("users")
public User getUserById(Long id) {
    return userRepository.findById(id).orElseThrow();
}

Make sure caching is enabled:

@EnableCaching
@SpringBootApplication
public class App {}

📡 9. Monitoring and Admin Commands¶

info                   # show metrics
dbsize                 # number of keys
monitor                # live command log
config get *           # view config
config rewrite          # persist config changes
slowlog get            # show slow commands

For real-time dashboards:

RedisInsight
redis-exporter for Prometheus / Grafana metrics.

🔒 10. Security & Performance Best Practices¶

Set a password (requirepass secret) — Redis is open by default.
Bind to localhost or internal networks (bind 127.0.0.1).
Disable FLUSHALL and CONFIG commands in production.
Use connection pooling for app clients.
For persistence: prefer AOF + fsync every second.
Enable maxmemory and maxmemory-policy allkeys-lru for safe eviction.

Example snippet:

maxmemory 512mb
maxmemory-policy allkeys-lru

💻 11. IDE & Tool Integration¶

JetBrains IDEs¶

Use built-in Database Tool Window → Add Data Source → Redis.
Visualize keys, TTLs, and values directly.
Supports EVAL and Lua scripting.

VS Code¶

Recommended extensions:

Redis Explorer → browse keys, TTLs, and memory usage.
REST Client → test APIs that interact with Redis.
.env files → store connection secrets.

Example .env:

REDIS_HOST=localhost
REDIS_PORT=6379
REDIS_PASSWORD=secret

🚀 12. CI/CD Integration Example¶

GitHub Actions — Redis as test dependency:

services:
  redis:
    image: redis:7
    ports: ['6379:6379']
    options: >-
      --health-cmd="redis-cli ping"
      --health-interval=5s --health-retries=5
steps:
  - uses: actions/checkout@v4
  - name: Run integration tests
    env:
      REDIS_HOST: localhost
      REDIS_PORT: 6379
    run: ./gradlew test

🧩 13. Real-World Patterns¶

Pattern	Description	Example
Cache-Aside	App reads from Redis; on miss, fetches DB + stores in Redis.	Common with Spring or Django.
Write-Through	Writes go to Redis and DB simultaneously.	Ensures consistency.
Pub/Sub	Services communicate via Redis channels.	Real-time notifications.
Streams	Event queue with consumer groups.	Great for jobs, analytics.

Example stream usage:

XADD jobs * type "email" user "alice"
XREADGROUP GROUP workers 1 COUNT 1 STREAMS jobs >

🧠 14. Troubleshooting¶

Issue	Fix
Redis not reachable	Check port 6379 and container health.
Keys disappear	TTL expired or memory eviction triggered.
“NOAUTH” error	Set password in config and client.
High latency	Tune `maxmemory` + eviction policy.
Data not persistent	Enable `appendonly yes`.

✅ 15. Summary¶

Redis = speed and simplicity — an in-memory data store with persistence options.
Ideal for caching, pub/sub, queues, and rate limiting.
Use Docker for easy setup and Compose for multi-service integration.
Always secure, monitor, and limit memory.
Combine with PostgreSQL for the best of both worlds: durability + velocity.

📄 File path suggestion:

docs/
└─ cheatsheets/
   └─ tools/
      └─ redis/
         └─ quick-refresher.md