Joey Umanito

Posted on Feb 27

Docker for Python Developers: From Zero to Containerized App

#docker #devops #python #tutorial

Docker changed how we deploy applications. No more "it works on my machine" problems. Here's everything a Python developer needs to know to get started with Docker.

Why Docker?

Before Docker:

"Works on my machine"
Complex environment setup
Dependency conflicts
Hard to scale

With Docker:

Consistent environments everywhere
One command setup
Isolated dependencies
Easy horizontal scaling

Your First Dockerfile

# Dockerfile
FROM python:3.11-slim

# Set working directory
WORKDIR /app

# Copy requirements first (for layer caching)
COPY requirements.txt .

# Install dependencies
RUN pip install --no-cache-dir -r requirements.txt

# Copy application code
COPY . .

# Expose port
EXPOSE 8000

# Run the application
CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]

Sample FastAPI App

# main.py
from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def read_root():
    return {"message": "Hello from Docker!"}

@app.get("/health")
def health_check():
    return {"status": "healthy"}

# requirements.txt
fastapi==0.104.1
uvicorn==0.24.0

Build and Run

# Build the image
docker build -t my-python-app .

# Run the container
docker run -p 8000:8000 my-python-app

# Run in background (detached)
docker run -d -p 8000:8000 my-python-app

# View running containers
docker ps

# Stop a container
docker stop <container_id>

Docker Compose for Multi-Service Apps

# docker-compose.yml
version: '3.8'

services:
  api:
    build: .
    ports:
      - "8000:8000"
    environment:
      - DATABASE_URL=postgresql://user:password@db:5432/mydb
    depends_on:
      - db
    volumes:
      - .:/app

  db:
    image: postgres:15
    environment:
      POSTGRES_USER: user
      POSTGRES_PASSWORD: password
      POSTGRES_DB: mydb
    volumes:
      - postgres_data:/var/lib/postgresql/data

  redis:
    image: redis:7-alpine
    ports:
      - "6379:6379"

volumes:
  postgres_data:

# Start all services
docker-compose up

# Start in background
docker-compose up -d

# Stop all services
docker-compose down

Essential Docker Commands

# Images
docker images                    # List images
docker pull python:3.11-slim     # Pull image
docker rmi my-image              # Remove image

# Containers
docker ps -a                     # List all containers
docker logs <container_id>       # View logs
docker exec -it <id> /bin/bash   # Shell into container
docker rm <container_id>         # Remove container

# Cleanup
docker system prune              # Remove unused resources

Environment Variables

import os

# In your Python app
DATABASE_URL = os.getenv("DATABASE_URL", "sqlite:///default.db")
API_KEY = os.getenv("API_KEY", "")
DEBUG = os.getenv("DEBUG", "False").lower() == "true"

# Pass env vars when running
docker run -e API_KEY=your_key -e DEBUG=true my-app

# Use .env file
docker run --env-file .env my-app

Production Best Practices

# Multi-stage build for smaller images
FROM python:3.11-slim AS builder
WORKDIR /app
COPY requirements.txt .
RUN pip install --user --no-cache-dir -r requirements.txt

FROM python:3.11-slim
WORKDIR /app
COPY --from=builder /root/.local /root/.local
COPY . .
ENV PATH=/root/.local/bin:$PATH
CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]

Free Hosting Options

Railway.app: Deploy Docker containers free
Render.com: Free tier for containerized apps
Fly.io: Generous free tier
Google Cloud Run: Pay only when running

Need Help Containerizing Your App?

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What Python apps are you containerizing with Docker? Share below!

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