Step-by-Step: The Docker Workflow for Beginners

Matthew

Docker makes it easy to package and run your apps anywhere — no more “it works on my machine.” In this post, we’ll go through the Docker workflow step by step, building a small Python app, running it in a container, and understanding how everything fits together.

Step 1 — Install Docker

Before we start, you need Docker installed on your machine.

  • Windows / macOS: Install Docker Desktop
    Follow the installer and make sure Docker is running (you’ll see a whale icon in your tray).
  • Linux: Install using your package manager. For example, on Ubuntu:
sudo apt update
sudo apt install docker.io
sudo systemctl start docker
sudo systemctl enable docker

Then verify it works:

docker --version

If you see a version number, you’re ready to go ✅

Step 2 — Create a Simple Python App

Let’s make a small Flask web app.

Create a new folder for your project:

mkdir docker-flask-demo
cd docker-flask-demo

Now create a file called app.py:

from flask import Flask

app = Flask(__name__)

@app.route("/")
def home():
    return "Hello from Docker!"
    
if __name__ == "__main__":
    app.run(host="0.0.0.0", port=5000)

Then create a requirements.txt file:

flask

This file tells Docker which Python packages your app needs.

Step 3 — Create a Dockerfile

In the same folder, create a new file called Dockerfile (no extension):

# Use an official Python base image
FROM python:3.11-slim

# Set the working directory
WORKDIR /app

# Copy files into the container
COPY requirements.txt .
RUN pip install -r requirements.txt
COPY . .

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

This file is like a recipe — it tells Docker how to build your app.

Step 4 — Build the Docker Image

Now that you have a Dockerfile, let’s build the image.

Run this command in the same folder:

docker build -t my-flask-app .
  • -t my-flask-app gives your image a name.
  • . means “build using the Dockerfile in the current folder.”

Step 5 — Run the Container

Start your container:

docker run -p 5000:5000 my-flask-app
  • -p 5000:5000 maps your computer’s port 5000 to the container’s port 5000.
  • my-flask-app is the image you just built.

Now open http://localhost:5000 in your browser.
You should see:

“Hello from Docker!”

🎉 Congratulations — your Python app is running in Docker!

Step 6 — Update and Rebuild

If you change your app (for example, the message in app.py), you’ll need to rebuild the image:

docker build -t my-flask-app .

Then re-run it:

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

💡 Pro tip: You can automate this with Docker Compose (we’ll cover that in a future post).

Step 7 — Share Your App (Optional)

You can share your app with anyone using Docker Hub.

  1. Log in: docker login
  2. Tag your image: docker tag my-flask-app yourname/my-flask-app:latest
  3. Push it: docker push yourname/my-flask-app:latest

Now anyone can run your app with:

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

Step 8 — Clean Up

When you’re done, you can stop and remove containers:

docker ps -a           # list containers
docker stop <id>       # stop one
docker rm <id>         # remove it
docker image prune     # delete old images

🧠 Step 9 — Recap

Let’s recap the Docker workflow:

  1. Write your app (app.py)
  2. Define dependencies (requirements.txt)
  3. Write a Dockerfile
  4. Build your image
  5. Run a container
  6. Rebuild and rerun as you update
  7. (Optional) Push to Docker Hub

That’s the core Docker workflow — build → run → share.

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