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Overview 📘

Docker — Overview & Quick Commands

Docker packages applications into portable containers. Below are the most-used commands and a few practical examples and best practices.

Quick Commands (common)

Command Description
docker build -t <image_name>:<tag> . Build an image from a Dockerfile in the current directory.
docker run -p <host>:<container> <image> Run a container and map ports.
docker ps -a List all containers (running and stopped).
docker logs <container> Show container logs.
docker exec -it <container> /bin/bash Open an interactive shell inside a running container.
docker images List local images.
docker rmi <image> Remove an image.
docker system prune Clean up unused resources.
docker pull <image> / docker push <image> Pull from / push to a registry.

Dockerfile best practices

  • Start from a small, maintained base image (e.g., python:3.11-slim).
  • Use multi-stage builds to keep final images small.
  • Pin dependency versions in requirements.txt or package manifests.
  • Minimize the number of layers by combining related RUN commands.
  • Avoid running as root in production containers; create a non-root user.
  • Add healthchecks for production services.

Example (multi-stage) Dockerfile snippet:

FROM node:18-alpine AS build
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

FROM nginx:stable-alpine
COPY --from=build /app/dist /usr/share/nginx/html
EXPOSE 80
HEALTHCHECK --interval=30s CMD curl -f http://localhost/ || exit 1

Docker Compose quick example

version: '3.8'
services:
    app:
        build: .
        ports:
            - "8080:80"
        environment:
            - NODE_ENV=production
    redis:
        image: redis:6-alpine
        volumes:
            - redis-data:/data

volumes:
    redis-data:

CI/CD tips for images

  • Build images in CI, tag with commit SHA and semantic tag, and push to a registry (ACR/ECR/GCR/Docker Hub).
  • Scan images for vulnerabilities (Trivy, Clair) as part of pipeline.
  • Use immutable tags for deployments (avoid latest in production).

If you want, I can add a runnable examples/docker-quickstart/ folder with a small sample app, Dockerfile, and a GitHub Actions pipeline next.