Deploying a Flask App to Google Cloud Run

In this tutorial, we will walk through the steps of creating a simple "Hello World" Flask application and deploying it to Google Cloud Run using Docker. This guide is specifically tailored for Windows users using Git Bash.

Prerequisites

Before you begin, ensure you have the following installed on your machine:

• Python 3.9 or later

• Git

• Git Bash (comes with Git for Windows)

• Google Cloud SDK

Step-by-Step Guide

1. Create Project Directory

First, create a new directory for your project and navigate into it.

mkdir hello-flask
cd hello-flask

2. Set Up a Virtual Environment

Create a virtual environment to manage your project's dependencies.

python -m venv env

Navigate into the env directory and activate the virtual environment.

cd env
source Scripts/activate

You should now see (env) at the beginning of your terminal prompt, indicating that the virtual environment is active.

3. Install Flask

Install Flask using pip.

pip install flask

Navigate back to your project root directory.

cd ..

4. Create the Flask App

Create a new file named app.py and add the following code:

from flask import Flask
app = Flask(__name__)

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

if __name__ == '__main__':
    app.run(debug=True)

5. Install Additional Dependencies

Install python-dotenv, Flask-CORS, and gunicorn.

pip install python-dotenv
pip install Flask-CORS
pip install gunicorn

6. Create a .env File

Create a .env file in the root directory of your project and add the following content:

FLASK_DEBUG=1

7. Update main.py

Update the contents of app.py to include environment variable loading and CORS support:

import os
from flask import Flask
from dotenv import load_dotenv
from flask_cors import CORS

# Load environment variables from .env file
load_dotenv()

app = Flask(__name__)
CORS(app)  # Enable CORS for all routes and origins

# Configure FLASK_DEBUG from environment variable
app.config['DEBUG'] = os.environ.get('FLASK_DEBUG')

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

if __name__ == '__main__':
    app.run()

8. Freeze Dependencies

Generate a requirements.txt file with all the necessary dependencies.

pip freeze > requirements.txt

9. Create app.yaml

Create an app.yaml file with the following content:

runtime: python39
entrypoint: gunicorn -b :$PORT app:app

10. Create Dockerfile

Create a Dockerfile with the following content, be sure to use a capital 'D' in Dockerfile and do not assign any file extension:

# Dockerfile
FROM python:3.9.17-bookworm
# Allow statements and log messages to immediately appear in the logs
ENV PYTHONUNBUFFERED True
# Copy local code to the container image.
ENV APP_HOME /back-end
WORKDIR $APP_HOME
COPY . ./

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

# Run the web service on container startup. Here we use the gunicorn
# webserver, with one worker process and 8 threads.
# For environments with multiple CPU cores, increase the number of workers
# to be equal to the cores available.
# Timeout is set to 0 to disable the timeouts of the workers to allow Cloud Run to handle instance scaling.
CMD exec gunicorn --bind :$PORT --workers 1 --threads 8 --timeout 0 app:app

11. Create a New Google Cloud Project

In your browser, visit the Google Cloud Console (https://console.cloud.google.com/) and create a new project.

12. Initialize Google Cloud SDK

If you haven't already installed the Google Cloud SDK:

(New-Object Net.WebClient).DownloadFile("https://dl.google.com/dl/cloudsdk/channels/rapid/GoogleCloudSDKInstaller.exe", "$env:Temp\GoogleCloudSDKInstaller.exe")

& $env:Temp\GoogleCloudSDKInstaller.exe

After installation, initialize it with the following command:

gcloud init

Follow the prompts to sign in and select the project you just created.

13. Deploy to Google Cloud Run

Deploy your application to Google Cloud Run:

gcloud run deploy --source .

Follow the prompts to specify a service name, choose a server region, and allow unauthenticated invocations. Your application should now be deployed, and you'll get a URL where your app is hosted.

Spinning down the server:

Make sure to replace [project-id] with your projects id and [region] with the region you selected earlier for your server.

gcloud run services delete [project-id] --region=[region]

OR

Visit https://console.cloud.google.com/run and select the project you wish to delete.

Need more help?

If you are having issues successfully deploying your flask app to Google Cloud Run, feel free to download the complete files for this tutorial by clicking on the link below:

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Conclusion

Congratulations! You have successfully created and deployed a "Hello World" Flask app to Google Cloud Run. You can now access your app via the URL provided by Google Cloud Run.

Feel free to customize your Flask application further and explore the various features offered by Google Cloud Run.