What is Docker?

What is Docker?

 Docker is a platform that lets you package your applications and all their dependencies into a single container so they run consistently across different environments.

it provide better approach to create and manage build to any platform

Think of it like this:

• Without Docker: "It works on my machine" problem happens because environments differ.

• With Docker: You send the same container image that runs exactly the same everywhere — laptop, server, or cloud.

Key points:

• Image = Blueprint/template of your app.

• Container = Running instance of that image.

• Dockerfile = Script with instructions to build an image.

• Registry – Storage for images (Docker Hub, AWS ECR, Azure ACR)

• Volume – Persistent storage for containers

• Network – Communication between containers

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2. Install Docker on Windows

1. Check your Windows Version
   Docker Desktop works best on Windows 10/11 Pro/Enterprise (with WSL2).
   If you have Windows Home, it also works but WSL2 is required.

2. Download Docker Desktop

   • Go to Docker official site

   • Download Docker Desktop for Windows.

3. Install Docker Desktop

   • Run the installer.

   • Make sure "Use WSL 2 instead of Hyper-V" is checked (for most systems).

   • Follow prompts and restart if required.

4. Enable WSL 2 (if not already)

   • Open PowerShell (Admin) and run:

     powershell
     
     wsl --install
     

   • Restart your system.

5. Verify Docker Installation
   Open Command Prompt or PowerShell:

   bash
   
   docker --version 
   

   You should see something like:

   nginx
   
   Docker version 27.0.3, build abc123

3. Basic Docker Commands

# Get images
docker images

# Pull image from Docker Hub
docker pull nginx

# Run container
docker run -d -p 8080:80 nginx

# List running containers
docker ps

# Stop container
docker stop <container_id>

# Remove container
docker rm <container_id>

# Remove image
docker rmi nginx

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3. Simple Example: Create & Build with Docker

We’ll create a simple Hello World Python app and run it in Docker.

Step 1 — Create a project folder

bash

mkdir docker-demo
cd docker-demo

Step 2 — Create app.py

python

# app.py
print("Hello from Docker!")

Step 3 — Create Dockerfile

dockerfile

# Use official Python image
FROM python:3.9

# Set working directory
WORKDIR /app

# Copy all files to container
COPY . /app

# Run the Python app
CMD ["python", "app.py"]

Step 4 — Build the Docker Image

bash

docker build -t my-python-app .

Here:

• -t my-python-app = Tag/name for your image.

• . = Build from current folder.

Step 5 — Run the Docker Container

bash

docker run my-python-app

You should see:

csharp

Hello from Docker!