From Virtual Machines to Docker Containers:

1. Virtual Machines (VMs)

A VM is a software-based simulation of a physical computer, running an OS on top of a hypervisor.

• Example: Running Windows inside Linux using VirtualBox.

• Key Components: Hypervisor, Guest OS, Virtualized Hardware.

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2. Containers vs. VMs

• Example: Instead of running multiple VMs with full OS installations, you can run lightweight containers sharing the host OS kernel.

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3. What is Docker?

Docker is a platform that allows you to build, ship, and run applications inside containers.

• Example: Running a Python app in a container without installing Python on your machine.

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4. Dockerfile

A script containing instructions to build a Docker image.

• Example Dockerfile:

    FROM python:3.9  
    WORKDIR /app  
    COPY . .  
    RUN pip install -r requirements.txt  
    CMD ["python", "app.py"]
  

• Explanation:

  • FROM → Base image (Python 3.9)

  • WORKDIR → Sets working directory

  • COPY → Copies files from host to container

  • RUN → Executes commands inside container

  • CMD → Runs application when container starts

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5. Docker Registry

A storage for Docker images.

• Public: Docker Hub

• Private: AWS ECR, Azure ACR, GitHub Container Registry

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6. Docker Architecture

• Docker Daemon: Background service managing containers.

• Container Runtime: Software responsible for running containers (e.g., containerd).

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7. Workflow: Build, Push, Pull, Run

1. Build Image: docker build -t myapp .

2. Push to Registry: docker push myrepo/myapp:latest

3. Pull on Another Machine: docker pull myrepo/myapp:latest

4. Run Container: docker run -d -p 5000:5000 myrepo/myapp

Conclusion:

In this session, we broke down the fundamentals of Docker and containerization, from understanding how VMs differ from containers to exploring Docker’s architecture and workflow. These notes offer a practical foundation for building, shipping, and running applications efficiently. Keep this guide handy as you continue your journey into DevOps, and get ready for more insights in our upcoming ReadList sessions. Happy learning!