Docker Security Best Practices For Developers

Containerization makes deployment faster and more consistent—but security should never be an afterthought. In this guide, we’ll explore essential Docker security best practices for developers, with a practical Python example to show how small changes can protect your app.

Why Docker Security Matters

Docker simplifies packaging applications and their dependencies. But with power comes responsibility—an insecure Docker image or container setup can expose your system or sensitive data to attacks.

1. Use Official and Minimal Base Images

Why? Smaller images have fewer packages—and fewer potential vulnerabilities.

❌ Avoid:

FROM ubuntu:latest

✅ Prefer:

FROM python:3.11-slim

The slim variant reduces the attack surface and avoids unnecessary packages.

2. Do Not Run as Root in Containers

By default, many containers run as root, which can be dangerous.

Example:

# Add a non-root user
RUN useradd -m appuser
USER appuser

You can also combine this with multi-stage builds for production readiness.

3. Keep Dependencies Locked

Avoid unexpected or malicious updates by pinning versions.

requirements.txt

Flask==2.3.2
requests==2.31.0

Dockerfile

COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

4. Use .dockerignore to Avoid Sensitive Files

Don’t accidentally copy .env, credentials, or .git folders into your image.

.dockerignore

*.env
.git
__pycache__/
*.pyc

This is similar to .gitignore, and helps reduce build context and leak risk.

5. Limit Container Capabilities

By default, containers get many Linux capabilities. You can restrict them:

docker run --cap-drop ALL --cap-add NET_BIND_SERVICE my-image

Or run in read-only mode:

docker run --read-only my-image

Complete Example (Secure Python API)

File Structure:

DockerSecurityPractice/
├── server.py
├── requirements.txt
├── Dockerfile

server.py

from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
    return 'Secure Flask API'

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=5000)

Dockerfile

FROM python:3.11-slim

RUN useradd -m appuser
WORKDIR /home/appuser

COPY requirements.txt ./
RUN pip install --no-cache-dir -r requirements.txt

COPY server.py ./
USER appuser

CMD ["python", "server.py"]

requirements.txt

Flask==2.3.2

Run securely

docker build -t secure-api .

docker run -p 5000:5000 --read-only --cap-drop ALL secure-api

Result:

Final Tips

Security in Docker isn’t automatic—but with the right steps, it’s achievable and effective. Following these best practices early in development helps avoid serious issues in staging or production.

You can read more useful articles like Docker Networking Basics: Bridge, Host, and Overlay Networks.

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