Running Redis via Docker Compose

Where we left off

Lesson 1 ran docker compose up -d redis and connected to whatever that started, without looking at the compose file itself. This lesson slows down on that file, and on why this course's image isn't plain redis.

One compose file, three databases

This project's docker-compose.yml (project root) defines three services: db (pgvector's Postgres), graph_db (pggraph's Postgres), and redis. They're independent containers on independent ports, so docker compose up -d with no service name would start all three at once; docker compose up -d redis starts only the one this course needs.

redis:
  image: redis/redis-stack-server:7.4.0-v3
  restart: unless-stopped
  environment:
    REDIS_ARGS: "--requirepass ${REDIS_PASSWORD:-redis}"
  ports:
    - "6379:6379"
  volumes:
    - redis_data:/data

6379 is Redis's default port, unlike pgvector's Postgres (remapped to 5433 to avoid clashing with a real Postgres install), there's rarely already something else on 6379, so no remapping is needed here. redis_data is a named volume, the same durability-of-the-container idea as pgvector_data: the container can be recreated without losing what's stored, until you explicitly delete the volume.

Why "stack", not plain redis

The official redis image ships only the core in-memory data structures this tier covers (strings, hashes, lists). redis-stack-server is the same core, plus modules bundled in: RedisJSON (Lesson 13) and RediSearch (Lessons 17-18, vector and hybrid search). Using the stack image from the start means Lesson 17 doesn't need a different container, everything this course needs is already running.

REDIS_ARGS and the password

REDIS_ARGS is how the stack image passes flags straight to the underlying redis-server process, here --requirepass, setting a password (redis, from .env's REDIS_PASSWORD, defaulting to redis if unset). A password on a local dev container mostly doesn't matter for security, it's here so this course can honestly teach requirepass in Lesson 22 against a server that already has it configured, rather than turning it on later and breaking every earlier lesson's connection string.

Confirming the modules loaded

r.execute_command("MODULE", "LIST")

redis-py has typed helpers for most commands (.ping(), .get(), and so on), but not every admin command has one, .execute_command() sends any command verbatim, the same escape hatch psycopg's conn.execute() provides for raw SQL. MODULE LIST returns every module the running server has loaded; this lesson's output should include search and ReJSON alongside Redis's own bundled modules.