Deploying a Python Flask application to Fly

In this tutorial you will learn how to deploy a containerized Python Flask application to Fly.

The final code of this article can be found here.

#Prerequisites

• A Fly account
• A computer with Python, Docker, and Flyctl (the Fly CLI)

#Creating the application

requirements.txt

Flask==2.1.0

server.py

from flask import Flask, jsonify
import random

application = Flask(__name__)

port = 8080


@application.route("/")
def hello():
   return jsonify({"message": "Hello, World!"})


@application.route("/random")
def generate_random_number():
   return jsonify({"number": random.randint(0, 100)})


if __name__ == "__main__":
   application.run(port=port)

#Containerizing the application

Dockerfile

FROM python:3.9-slim-buster

WORKDIR /usr/src/app

COPY requirements.txt .

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

COPY . /usr/src/app

ENV FLASK_APP=server.py

EXPOSE 8080

CMD ["flask", "run", "--host", "0.0.0.0", "--port", "8080"]

To build and run the container locally:

docker build . -t hello-world
docker run -dp 8080:8080 hello-world

#Deploying the application

1. fly launch to prepare your fly.toml file, containing your project settings. Inside the fly.toml file, ensure the service's internal_port (8080 by default) matches the port exposed by your container.
2. fly deploy to deploy your application.
3. fly open to open the deployed application in your browser.

#Cleaning up

fly destroy your-unique-app-id -y removes your application from the Fly platform.

That's all! Don't forget to delete the application once you're done testing.

The final code of this article can be found here.