Dockerizing a FastAPI App: Eliminating 'It Works on My Machine'

Source: Dev.to

What is Docker?

Docker packages your app and all its dependencies into a container—a lightweight, portable unit that runs exactly the same on any machine. No more “it works on my machine” problems.

The Dockerfile

FROM python:3.11-slim
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
COPY . .
EXPOSE 8000
CMD ["python", "-m", "uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]

Line by line:

• FROM → base image (Python 3.11)
• WORKDIR → working directory inside the container
• COPY requirements.txt → copy dependencies first
• RUN pip install → install dependencies
• COPY . . → copy all app code
• EXPOSE 8000 → open port 8000
• CMD → command to start the app

docker-compose.yml

services:
  api:
    build: .
    ports:
      - "8000:8000"
    command: python -m uvicorn main:app --host 0.0.0.0 --port 8000

Docker Compose links services together, which becomes handy when you add a database container later.

Build & Run

docker build -t gdgoc-bowen-api .
docker-compose up --build

Proof it Builds

Lessons Learned

Docker is not just a DevOps tool; it’s a backend developer’s best friend. Every production app runs in containers today. Learning Docker early puts you ahead of most developers.

Day 19 done. 11 more to go.