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

#webdev #python #docker #backend

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 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
useful 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.

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