Introduction to Docker

What is Docker?

  • Docker is a tool that helps you package and run applications in a special environment called a container.
  • Think of a container as a box that holds everything your application needs to run—code, libraries, and settings—so it works the same everywhere.

Why Use Docker?

  • Consistency: Ensures your application works the same on all machines.
  • Simplifies Deployment: Makes it easy to share and deploy applications.
  • Resource Efficiency: Uses less system resources compared to virtual machines.
  • Scalability: Easily scale up or down by running more or fewer containers.

Containers vs. Virtual Machines

Containers:

  • Lightweight: Share the host system's operating system.
  • Fast Startup: Launch in seconds.
  • Resource-Efficient: Use less memory and storage.

Virtual Machines:

  • Heavyweight: Include a full guest operating system.
  • Slower Startup: Take minutes to boot.
  • Isolated: Better security due to complete separation.

Advantages and Disadvantages of Docker

Advantages:

  • Solves Dependency Issues: Packages all dependencies with the app.
  • Cross-Platform: Runs on Windows, macOS, and Linux.
  • Scalable: Easily handle increased load by adding more containers.
  • Efficient Resource Use: No need for extra OS overhead.

Disadvantages:

  • Limited GUI Support: Not ideal for applications with graphical interfaces.
  • Windows Support: Not as robust as Linux support.
  • Security Concerns: Less isolated than virtual machines.
  • Requires Host OS: Can't run directly on hardware without an OS.

Docker Architecture

  • Docker uses a client-server architecture:

Components:

  • Docker Client (CLI): The command-line tool you use to interact with Docker.
  • Docker Daemon (Server): Runs in the background and does the heavy lifting (building, running, and distributing containers).
  • Docker Registry: Stores Docker images (e.g., Docker Hub).

Getting Started with Docker

  • Install Docker

    • Windows/macOS: Download from Docker's official website.
    • Linux: Use your package manager (e.g., sudo apt install docker.io for Ubuntu).

  • Verify Installation

docker --version
  • Run Your First Container
docker run hello-world

  • Understand Docker Images and Containers

  • Image: A snapshot of an application and its environment.

  • Container: A running instance of an image.

  • Pull an Image from Docker Hub

docker pull python:3.8-slim

Step 6: Run a Container Interactively

docker run -itd python:3.8-slim bash

Step 7: Exit the Container

  • Type exit or press Ctrl+D to exit the container.

Step 8: List Running Containers

docker ps

Step 9: Stop and Remove Containers

  • Stop a Container:
docker stop $(docker ps -q --filter "ancestor=python:3.8-slim")
  • Remove a Container:
docker rm $(docker ps -a -q --filter "ancestor=python:3.8-slim")

Step 10: Remove Images

docker rmi python:3.8-slim

Conclusion

  • Docker simplifies the process of developing, shipping, and running applications by using containers. It's a valuable tool for both developers and system administrators, making applications more portable and efficient.

Additional Resources