Docker

1. Introduction to Docker

Docker is a platform for developing, shipping, and running applications in containers. Containers allow developers to package an application with all its dependencies and configurations, ensuring it works consistently across different environments.

2. Key Concepts

Container: A lightweight, standalone, executable package that includes everything needed to run an application.
Image: A read-only template used to create containers.
Dockerfile: A text file containing instructions to build a Docker image.
Docker Hub: A cloud-based registry for sharing and storing Docker images.
Docker Compose: A tool for defining and running multi-container Docker applications.

3. Installing Docker

For Windows and Mac: Download Docker Desktop from the official website.
For Linux: Use your distribution's package manager or follow the official installation guide.

4. Basic Docker Commands

docker run: Create and start a container
docker pull: Download an image from a registry
docker build: Build an image from a Dockerfile
docker ps: List running containers
docker images: List available images
docker stop: Stop a running container
docker rm: Remove a container
docker rmi: Remove an image

5. Creating a Dockerfile

A Dockerfile typically includes:

Base image (FROM)
Working directory (WORKDIR)
Copying files (COPY)
Running commands (RUN)
Exposing ports (EXPOSE)
Setting environment variables (ENV)
Specifying the command to run (CMD)

Example Dockerfile:

FROM node:14
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
EXPOSE 3000
CMD ["node", "app.js"]

6. Building and Running Images

Build: docker build -t myapp:1.0 .
Run: docker run -p 3000:3000 myapp:1.0

7. Docker Compose

Docker Compose allows you to define multi-container applications in a YAML file.

Example docker-compose.yml:

version: '3'
services:
  web:
    build: .
    ports:
      - "3000:3000"
  db:
    image: mongo:latest
    volumes:
      - ./data:/data/db

Run with: docker-compose up

8. Docker Networking

Bridge: Default network driver
Host: Removes network isolation between container and host
Overlay: Connects multiple Docker daemons
Macvlan: Assigns a MAC address to a container

9. Docker Volumes

Volumes are used for persistent data storage:

Create: docker volume create myvolume
Use: docker run -v myvolume:/app/data myapp:1.0

10. Docker Security Best Practices

Use official base images
Scan images for vulnerabilities
Limit container resources
Use non-root users inside containers
Implement network segmentation

11. Docker in Production

Orchestration tools: Kubernetes, Docker Swarm
Monitoring: Prometheus, Grafana
Logging: ELK stack (Elasticsearch, Logstash, Kibana)

12. Advanced Topics

Multi-stage builds
Docker content trust
Docker registry
CI/CD integration

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