Dockerizing Flask Application: A Step-by-Step Guide

Introduction
What is Docker, and Why is it Needed?
Dockerizing your Flask Application
Step 1: Create a Flask Application
Step 2: Create a Dockerfile
Step 3: Build the Docker Image
Step 4: Run the Docker Container
Conclusion
Related Links

Introduction

You have probably heard about Docker a lot already. Docker is an open-source "containerization" platform that allows you to package and deploy applications in a portable and scalable way. Dockerizing your Flask application has several benefits, including improved consistency, faster deployment, and simplified dependencies management.

In this blog post, we will give you a little idea on what Docker is, why it is needed and then we'll explain a step-by-step guide on how to Dockerize your Flask application.

What is Docker, and Why is it Needed?

Docker is a runtime that allows you to run containers. A container is a lightweight, standalone executable package that contains everything the application needs to run, including the code, runtime, libraries, and system tools. The container provides an isolated environment that guarantees consistency and reproducibility, making it easier to deploy and manage applications across different environments.

Docker containers are also scalable and portable, which means you can deploy them on any platform or infrastructure, whether it's your local machine, a cloud provider, or a hybrid environment. Containers can also be versioned, which means you can track and roll back changes easily, making it easier to maintain and update your application.

Dockerizing your Flask Application

Before we start, make sure you have Docker installed on your system. You can download and install Docker :

using our beginner-friendly guide on How to Install docker on Ubuntu/Debian
from the official website https://www.docker.com/.

Step 1: Create a Flask Application

For the purpose of this tutorial, we will create a simple Flask application. If you already have an existing Flask application, you can skip this step.

To create a new Flask application, follow these steps:

Open a terminal and create a new directory for your application.
```
mkdir myflaskapp
cd myflaskapp
```
Create a new virtual environment for your application.
```
python3 -m venv venv
source venv/bin/activate
```

Install Flask and create a new file app.py with the following code:

from flask import Flask

app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello World!"

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

Run the application using the following command:
```
flask run
```
Open a web browser and navigate to http://localhost:5000/ to see the "Hello World!" message.

Step 2: Create a Dockerfile

A Dockerfile is a script that contains instructions on how to build a Docker image. To create a Dockerfile for our Flask application, follow these steps:

Create a new file named Dockerfile in the root directory of your Flask application.
Add the following content to the Dockerfile:

FROM python:3.9-slim-buster

WORKDIR /app

COPY requirements.txt requirements.txt
RUN pip install --no-cache-dir -r requirements.txt

COPY . .

EXPOSE 5000

CMD ["python", "app.py"]

Let's go through each line of the Dockerfile:

FROM python:3.9-slim-buster specifies the base image for our container. We will use Python 3.9 with a slim version of Debian Buster as the base image.
WORKDIR /app sets the working directory to /app.
COPY requirements.txt requirements.txt copies the requirements.txt file from the current directory to the /app directory in the container.
RUN pip install --no-cache-dir -r requirements.txt installs the Python dependencies listed in the requirements.txt file.
COPY . . copies the entire content of the current directory to the /app directory in the container.
EXPOSE 5000 exposes port 5000, which is the port that the Flask application is running on.
CMD ["python", "app.py"] specifies the command to run when the container starts. In this case, we are running the app.py file using Python.

Step 3: Build the Docker Image

To build the Docker image, run the following command in the same directory as the Dockerfile:

docker build -t myflaskapp .

This command builds a new Docker image with the tag myflaskapp. The . at the end of the command specifies that the build context is the current directory.

Step 4: Run the Docker Container

To run the Docker container, run the following command:

docker run -p 5000:5000 myflaskapp

This command starts a new Docker container using the myflaskapp image we built earlier. The -p flag maps port 5000 from the container to port 5000 on the host machine.

Open a web browser and navigate to http://localhost:5000/ to see the "Hello World!" message.

Conclusion

And there you go! Now you've learnt how to create a docker image for your flask application and run it. Dockerizing your Flask application can provide several benefits, including improved consistency, faster deployment, and simplified dependencies management.

In this tutorial, we provided a step-by-step guide on how to Dockerize your Flask application. We hope you found this tutorial helpful, and if you have any questions or comments, feel free to leave them below.

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