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Frameworks › Flask

Deploy a Flask App to Heroku

Deploy a Flask app with an encrypted .env.vault file to Heroku.

Find a complete code example on GitHub for this guide.

Initial setup

Install flask and gunicorn.

pip install --upgrade flask gunicorn

Create an index.py file with the web server code.

index.py

import os
from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello():
  hello = os.getenv("HELLO")
  return f"Hello {hello}"

Create your wsgi.py file.

wsgi.py

from index import app

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

Add a Procfile to run your app on Heroku.

Procfile

web: gunicorn --workers 4 --bind 0.0.0.0:${PORT} wsgi:app

Create runtime.txt.

runtime.txt

python-3.9.13

Freeze your requirements.txt.

pip freeze > requirements.txt

Set up your .gitignore file.

.gitignore

.DS_Store
.env
.flaskenv
*.pyc
*.pyo
env/
venv/
.venv/
env*
dist/
build/

Commit that to code and push it to Heroku.

heroku create
git push heroku
yourapp.herokuapp.com

Once deployed, your app will say 'Hello None' as it doesn't have a way to access the environment variable yet. Let's do that next.

Install python-dotenv-vault

Install python-dotenv-vault.

pip install --upgrade python-dotenv-vault

Create a .env file in the root of your project.

.env

# .env
HELLO="World"

As early as possible in your application, import and configure dotenv-vault.

index.py

from dotenv_vault import load_dotenv
load_dotenv()

import os
from flask import Flask
...

Try running it locally.

gunicorn --workers 4 --bind 0.0.0.0:3000 wsgi:app
[2023-07-31 10:20:35 -0700] [49163] [INFO] Starting gunicorn 20.1.0
[2023-07-31 10:20:35 -0700] [49163] [INFO] Listening at: http://0.0.0.0:3001 (49163)

It should say Hello World.

Great! os.environ now has the keys and values you defined in your .env file. That covers local development. Let's solve for production next.

Build .env.vault

Push your latest .env file changes and edit your production secrets. Learn more about syncing

npx dotenv-vault@latest push
npx dotenv-vault@latest open production

Use the UI to configure those secrets per environment.

www.dotenv.org

Then build your encrypted .env.vault file.

npx dotenv-vault@latest build

Its contents should look something like this.

.env.vault

#/-------------------.env.vault---------------------/
#/         cloud-agnostic vaulting standard         /
#/   [how it works](https://dotenv.org/env-vault)   /
#/--------------------------------------------------/

# development
DOTENV_VAULT_DEVELOPMENT="/HqNgQWsf6Oh6XB9pI/CGkdgCe6d4/vWZHgP50RRoDTzkzPQk/xOaQs="
DOTENV_VAULT_DEVELOPMENT_VERSION=2

# production
DOTENV_VAULT_PRODUCTION="x26PuIKQ/xZ5eKrYomKngM+dO/9v1vxhwslE/zjHdg3l+H6q6PheB5GVDVIbZg=="
DOTENV_VAULT_PRODUCTION_VERSION=2

Set DOTENV_KEY

Fetch your production DOTENV_KEY.

npx dotenv-vault@latest keys production
# outputs: dotenv://:[email protected]/vault/.env.vault?environment=production

Set DOTENV_KEY on Heroku using the CLI.

heroku config:set DOTENV_KEY='dotenv://:key_1234…@dotenv.org/vault/.env.vault?environment=production'

Or use Heroku's UI.

www.heroku.com

Deploy

Commit those changes safely to code and deploy.

That's it! On deploy, your .env.vault file will be decrypted and its production secrets injected as environment variables‚ just in time.

yourapp.herokuapp.com

You'll know things worked correctly when you see Loading env from encrypted .env.vault in your logs. If a DOTENV_KEY is not set (for example when developing on your local machine) it will fall back to standard dotenv functionality.

heroku logs --tail

You succesfully used the new .env.vault standard to encrypt and deploy your secrets. This is much safer than scattering your secrets across multiple third-party platforms and tools. Whenever you need to add or change a secret, just rebuild your .env.vault file and redeploy.