Guide to the Basics of Docker for DevOps

In the dynamic world of software development, Docker has emerged as a powerful tool for simplifying application deployment through containerization. This guide will walk you through the basics of Docker using simple examples to help you get started on your containerization journey.

1. Installation

Begin by installing Docker on your machine. Visit the official Docker website and follow the instructions for your specific operating system.

2. Hello World Example:

Create a simple "Hello World" Docker container using the following steps:

Step 1: Create a Dockerfile

        
    # Dockerfile
    FROM alpine:latest
    CMD echo "Hello, Docker World!"
    

This Dockerfile uses the Alpine Linux base image and specifies a command (`CMD`) to print the "Hello, Docker World!" message.

Step 2: Build the Docker Image

Open a terminal, navigate to the directory containing your Dockerfile, and run the following command:

        
    docker build -t hello-docker
    

This command builds a Docker image named `hello-docker` using the instructions in the Dockerfile.

Step 3: Run the Docker Container

Once the image is built, run the following command to start a container based on that image:

        
    docker run hello-docker
    

You should see the "Hello, Docker World!" message printed in the terminal.

3. Explore Docker Hub:

Visit Docker Hub to discover and use pre-built images for popular applications. Let's pull and run a simple Nginx web server as an example:

Step 1: Pull the Nginx Image

        
    docker pull nginx:latest
    

This command downloads the latest Nginx image from Docker Hub.

Step 2: Run the Nginx Container

        
    docker run -d -p 8080:80 --name my-nginx nginx:latest
    

This command runs an Nginx container in the background, mapping port 8080 on your host to port 80 in the container.

Now, if you open a web browser and navigate to `http://localhost:8080`, you should see the default Nginx welcome page.

4. Docker Compose Example:

Create a simple Docker Compose file (`docker-compose.yml`) to define a multi-container application:

        
    version: '3'
    services:
        web:
            image: nginx:alpine
            ports:
            - "8080:80"
        app:
            image: busybox
            command: echo "Hello from the app container!"
    

Run the following command to start both containers defined in the Docker Compose file:

        
    docker-compose up

This will start a Nginx container and a BusyBox container, each serving its purpose.

These examples provide a glimpse into the power and simplicity of Docker. As you explore further, you'll discover how Docker's containerization facilitates consistency, portability, and scalability in your development and deployment workflows.