Day 17 DevOps Task: Hands-on Docker Project for Engineers

Ever wonder how your favorite apps and websites run smoothly, no matter where you access them from? 🌐 Well, a lot of that magic happens behind the scenes with tools like Docker! Think of Docker as a little box 📦 that holds your entire app and all the stuff it needs to run—no more "it works on my machine" headaches! 😅

In this blog, we're diving into the Dockerfile 📝—the blueprint that tells Docker how to build your app’s container. And guess what? We’re not just talking about it; we’re actually building something cool! 💻✨

Here's what we’ll do:

🔹 Create a magical file called a Dockerfile 📝—it’s like a recipe for your web app!
🔹 Build your very own Docker image 📸 (a snapshot of your app).
🔹 Run it in a container and see it come to life in your web browser 🌐.
🔹 Finally, we’ll push it to a Docker Hub repository (a public or private app store for containers) for the world—or just you—to use! 🏢✨

Sounds exciting? 🙌 Grab your favorite beverage ☕, fire up your terminal 💻, and let’s Dockerize our first app together!

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🛠️ Prerequisites

Before we start, make sure you’ve got the following set up:

1. Basic knowledge of web applications 🌐 (Don’t worry, you won’t need to be a coding ninja 🥷)

2. Docker installed on your machine 🐳

   If you haven’t installed Docker yet, head over to Docker Installation and get it up and running. It’s super easy!

3. A Docker Hub Account
   If you want to share your app with the world, you’ll need to push your Docker image to a repository like Docker Hub. Don’t have an account? Sign up here.

Got all that? Awesome! Let’s dive into the magic of Dockerfiles and containers.✨

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TASKS

• Create a Dockerfile for a simple web application (e.g. a Node.js or Python app)

• Build the image using the Dockerfile and run the container

• Verify that the application is working as expected by accessing it in a web browser

• Push the image to a public or private repository (e.g. Docker Hub)

Step 1: Create a Dockerfile

Let’s start by creating a simple Python web application using Flask (a lightweight web framework).

1.1. Project Structure 🏗️

my-simple-app/
├── app.py          # Python web app file
└── Dockerfile      # Our secret recipe file!

Create a folder named my-simple-app and navigate into it:

mkdir my-simple-app && cd my-simple-app

1.2. app.py (Our Web App Code) 🧑‍💻

Create a file called app.py and paste this code:

from flask import Flask

app = Flask(__name__)

@app.route("/")
def home():
    return "Hello, World! 🌍 Welcome to my Dockerized Web App."

if __name__ == "__main__":
    app.run(host="0.0.0.0", port=5000)

Create a requirements.txt file to list the dependencies:

Flask==3.1.0

This little Python app displays "Hello, World!" when you visit it in a web browser. 🌐

1.3. Dockerfile (Our Recipe) 📜

Now, create a file named Dockerfile in the same folder and add this code:

# Step 1: Use an official Python image as the base
FROM python:3.9-slim

# Step 2: Set the working directory inside the container
WORKDIR /app

# Step 3: Copy the app code into the container
COPY . .

# Step 4: Install Flask (our web framework)
RUN pip install -r requirements.txt

# Step 5: Expose the port that Flask will use
EXPOSE 5000

# Step 6: Define the command to run the app
CMD ["python", "app.py"]

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🔨 Step 2: Build the Docker Image

Think of this step as turning your recipe into a ready-to-serve dish. 🍲
Run the following command in the terminal inside the my-simple-app directory:

docker build -t my-web-app:1.0 .

• docker build: Builds a Docker image.

• -t my-web-app:1.0: Tags the image with the name my-web-app and version 1.0.

• .: Tells Docker to look for the Dockerfile in the current directory.

⏳ After a few seconds, your image will be ready! 🎉

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🚀 Step 3: Run the Docker Container

Let’s run our web app inside a Docker container.

docker run -d -p 5000:5000 my-web-app:1.0

• -d: Runs the container in detached mode (in the background).

• -p 5000:5000: Maps port 5000 on your computer to port 5000 in the container.

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🌐 Step 4: Verify the App in a Browser

Open your favorite browser and go to:
👉 localhost:5000

You should see:
"Hello, World! 🌍 Welcome to my Dockerized Web App." 🎉

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📤 Step 5: Push the Image to Docker Hub

Finally, Let’s share our image with the world! 🌍

5.1. Log in to Docker Hub

docker login

Enter your Docker Hub username and password.

5.2. Tag the Image

docker tag my-web-app:1.0 <your-dockerhub-username>/my-web-app:1.0

5.3. Push the Image

docker push <your-dockerhub-username>/my-web-app:1.0

✅ Your image is now available on Docker Hub! 🎉 Anyone can pull and run it with:

docker pull <your-dockerhub-username>/my-web-app:1.0
docker run -p 5000:5000 <your-dockerhub-username>/my-web-app:1.0

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🎉 And That’s a Wrap!

You’ve successfully:
✅ Created a Dockerfile for a web app
✅ Built a Docker image
✅ Ran a container to host the app
✅ Verified it in a browser
✅ Pushed the image to Docker Hub

Now, you can confidently say: “It works on every machine!” 💪

Happy Dockering! 🐳✨