Yash Sonawane

Posted on Mar 2

Getting Started with Docker: How to Containerize Your First Application

🚀 Why Docker?

Ever heard someone say, "It works on my machine" while debugging a nightmare in production? Yeah, we've all been there. Docker eliminates this problem by containerizing your applications—ensuring they run the same everywhere, from your local laptop to a massive cloud deployment.

If you're a DevOps enthusiast or a developer aiming to streamline deployments, mastering Docker is a game-changer. So, let’s cut the fluff and jump straight into containerizing your first application.

🛠 Step 1: Install Docker

Before diving in, you need Docker installed. If you haven’t already:

Windows & Mac: Install Docker Desktop
Linux: Use the following commands to install:

  sudo apt update
  sudo apt install docker.io -y
  sudo systemctl enable --now docker

Verify installation:

  docker --version

📦 Step 2: Create Your First Application

Let’s keep it simple with a Python Flask app.

1️⃣ Create a new project folder:

mkdir my-docker-app && cd my-docker-app

2️⃣ Create app.py:

from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
    return "Hello, Docker!"

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

3️⃣ Add requirements.txt:

flask

🛳 Step 3: Write a Dockerfile

A Dockerfile is a blueprint for creating Docker containers. Create a file named Dockerfile (no extension) and add:

# Use an official Python runtime as a parent image
FROM python:3.9

# Set the working directory in the container
WORKDIR /app

# Copy the current directory contents into the container at /app
COPY . .

# Install any dependencies
RUN pip install -r requirements.txt

# Make port 5000 available
EXPOSE 5000

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

⚙️ Step 4: Build and Run the Container

Let’s bring this to life! Run the following command to build the image:

docker build -t my-flask-app .

Once the image is built, start a container:

docker run -p 5000:5000 my-flask-app

🎉 Boom! Your Flask app is now running inside a Docker container. Open http://localhost:5000 in your browser to see it in action.

🔥 Step 5: Share Your Container (Optional but Cool)

Want to share your containerized app? Push it to Docker Hub:

docker login

docker tag my-flask-app your-dockerhub-username/my-flask-app

docker push your-dockerhub-username/my-flask-app

Now, anyone can run your app with:

docker run -p 5000:5000 your-dockerhub-username/my-flask-app

📌 Step 6: Manage Containers

Now that you have a running container, let’s explore some useful commands:

List running containers:

  docker ps

List all containers (including stopped ones):

  docker ps -a

Stop a running container:

  docker stop <container_id>

Remove a container:

  docker rm <container_id>

🏗 Step 7: Use Docker Compose

For multi-container applications, Docker Compose is your best friend. Create a docker-compose.yml file:

version: '3'
services:
  web:
    build: .
    ports:
      - "5000:5000"

Run your app with:

docker-compose up

🧹 Step 8: Clean Up Docker Resources

Docker can consume disk space quickly. Use these commands to clean up:

Remove all stopped containers:

  docker container prune

Remove unused images:

  docker image prune -a

Remove all unused volumes:

  docker volume prune

🔑 Step 9: Run Containers in Detached Mode

Running a container in the background ensures it doesn’t block your terminal:

docker run -d -p 5000:5000 my-flask-app

Check logs of a running container:

docker logs <container_id>

🔥 Step 10: Deploy Containers to the Cloud

Once you're comfortable running containers locally, try deploying them to the cloud using:

AWS ECS (Elastic Container Service)
Google Cloud Run
Azure Container Apps
Kubernetes for large-scale orchestration

💡 Final Thoughts

Docker is a must-have skill for modern developers and DevOps engineers. With just a few commands, you’ve successfully containerized your first app. Now, imagine scaling this up with Kubernetes, CI/CD, and cloud deployments! 🚀

What’s Next?