Multi-Container Application — Flask + Redis

The problem

A web application that keeps state in its own process loses that state the moment the container restarts or scales. The counter needed to live outside the app container, in a dedicated data service the app reaches over the container network rather than over a hardcoded address.

What I built

1. 01

   Wrote a Flask application with two routes: / rendering the dashboard and welcome view, and /count incrementing and reading a visit counter stored in Redis.

2. 02

   Containerized the app with a slim python:3.11-slim Dockerfile — WORKDIR, COPY, pip install flask redis, EXPOSE 5003 and a CMD entrypoint.

3. 03

   Declared both services in docker-compose.yml: a redis:7-alpine service started with --requirepass and its port published, and the built web service with depends_on ordering.

4. 04

   Passed REDIS_HOST, REDIS_PORT and REDIS_PASSWORD as environment variables so the Flask container resolves the database by service name through Compose's internal DNS instead of an IP address.

5. 05

   Configured a Redis volume for persistent storage so the counter survives container restarts, then verified live increments by refreshing /count.