Deploying python-flask API on heroku

Jalaz Kumar · July 11, 2020

Deployment   Python   Heroku

Terminology

  • virtualenv: A tool to create isolated Python environments
  • flask: A micro web framework written in Python. It is classified as a microframework because it does not require particular tools or libraries. It has no database abstraction layer, form validation, or any other components where pre-existing third-party libraries provide common functions.
  • heroku: A cloud platform as a service supporting several programming languages.
  • pip: A de facto standard package-management system used to install and manage software packages written in Python.

Creating a flask API locally

Step 1: Initialise virtualenv for the flask API

jalaz@jalaz-personal:~/tech/assets/demos/flask-heroku$ virtualenv venv
Using base prefix '/usr'
New python executable in /tech/assets/demos/flask-heroku/venv/bin/python3
Not overwriting existing python script /tech/assets/demos/flask-heroku/venv/bin/python (you must use /tech/assets/demos/flask-heroku/venv/bin/python3)
Installing setuptools, pip, wheel...
done.

Step 3: Activate the virtualenv & install flask using

jalaz@jalaz-personal:~/tech/assets/demos/flask-heroku$ source venv/bin/activate
(venv) jalaz@jalaz-personal:~/tech/assets/demos/flask-heroku$ pip install flask
Collecting flask
  Using cached Flask-1.1.2-py2.py3-none-any.whl (94 kB)
Collecting Jinja2>=2.10.1
  Using cached Jinja2-2.11.2-py2.py3-none-any.whl (125 kB)
Collecting itsdangerous>=0.24
  Using cached itsdangerous-1.1.0-py2.py3-none-any.whl (16 kB)
Collecting Werkzeug>=0.15
  Using cached Werkzeug-1.0.1-py2.py3-none-any.whl (298 kB)
Collecting click>=5.1
  Downloading click-7.1.2-py2.py3-none-any.whl (82 kB)
     |████████████████████████████████| 82 kB 16 kB/s
Collecting MarkupSafe>=0.23
  Using cached MarkupSafe-1.1.1-cp37-cp37m-manylinux1_x86_64.whl (27 kB)
Installing collected packages: MarkupSafe, Jinja2, itsdangerous, Werkzeug, click, flask
Successfully installed Jinja2-2.11.2 MarkupSafe-1.1.1 Werkzeug-1.0.1 click-7.1.2 flask-1.1.2 itsdangerous-1.1.0

Step 3: Create a main.py file with the following content

from flask import Flask
app = Flask(__name__)


@app.route('/')
def intro():
    return "Flask App Running...!"

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

Step 4: Run the flask app using python app.py

(venv) jalaz@jalaz-personal:~/tech/assets/demos/flask-heroku$ python app.py
 * Serving Flask app "app" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

Step 5: On hitting, localhost:5000, if you get Flask App Running…!. Kudos, You got your flask API running locally.

Using already created flask API

Step 1: Get local copy of the project using

wget https://github.com/jaykay12/tech/assets/demos/flask-heroku.zip

Step 2: Create a virtualenv for the python web app using

virtualenv venv

Step 3: Activate the virtualenv using

source venv/bin/activate

Step 4: Install all the python packages using

pip install -r requirements.txt

Step 5: Run the flask app using python app.py

(venv) jalaz@jalaz-personal:~/tech/assets/demos/flask-heroku$ python app.py
 * Serving Flask app "app" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

Step 5: On hitting, localhost:5000, if you get Flask App Running…!. Kudos, You got your flask API running locally.

Deploying on Heroku

Step 1: Logging into Heroku using heroku cli

jalaz@jalaz-personal:~/tech/assets/demos/flask-heroku$ heroku login
heroku: Press any key to open up the browser to login or q to exit:
Opening browser to https://cli-auth.heroku.com/auth/cli/browser/xxxx-xxx-xxx
Logging in... done
Logged in as jalazkumar1208@gmail.com

Login Success

Step 2: Create a heroku app inside the directory

jalaz@jalaz-personal:~/tech/assets/demos/flask-heroku$ heroku create flask-heroku-jalaz
Creating ⬢ flask-heroku-jalaz... done
https://flask-heroku-jalaz.herokuapp.com/ | https://git.heroku.com/flask-heroku-jalaz.git

Step 3: Set Buildpacks for the app

jalaz@jalaz-personal:~/tech/assets/demos/flask-heroku$ heroku buildpacks:set heroku/python --app flask-heroku-jalaz
Buildpack set. Next release on flask-heroku-jalaz will use heroku/python.
Run git push heroku master to create a new release using this buildpack.

Step 4: Create requirements.txt file for the project if it doesn’t exist using pip freeze > requirements.txt

Step 5: Create a Procfile with the following content.

web: gunicorn app:app

Procfile: A text file in the root directory of your application, to explicitly declare what command should be executed to start your app

Step 6: Commit these new deployment changes.

jalaz@jalaz-personal:~/tech/assets/demos/flask-heroku$ git status
On branch master
Untracked files:
  (use "git add <file>..." to include in what will be committed)

	Procfile
nothing added to commit but untracked files present (use "git add" to track)
jalaz@jalaz-personal:~/tech/assets/demos/flask-heroku$ git add Procfile
jalaz@jalaz-personal:~/tech/assets/demos/flask-heroku$ git commit -m "Added Procfile"
[master 1210ae4] Added Procfile
 1 file changed, 1 insertion(+)
 create mode 100644 Procfile

Step 7: Push to deploy.

jalaz@jalaz-personal:~/tech/assets/demos/flask-heroku$ git push heroku master
Enumerating objects: 10, done.
Counting objects: 100% (10/10), done.
Delta compression using up to 4 threads
Compressing objects: 100% (8/8), done.
Writing objects: 100% (10/10), 1001 bytes | 500.00 KiB/s, done.
Total 10 (delta 1), reused 0 (delta 0)
remote: Compressing source files... done.
remote: Building source:
remote:
remote: -----> Python app detected
remote: -----> Installing python-3.6.11
remote: -----> Installing pip
remote: -----> Installing SQLite3
remote: -----> Installing requirements with pip
remote:        Collecting click==7.1.2
remote:          Downloading click-7.1.2-py2.py3-none-any.whl (82 kB)
remote:        Collecting Flask==1.1.2
remote:          Downloading Flask-1.1.2-py2.py3-none-any.whl (94 kB)
remote:        Collecting itsdangerous==1.1.0
remote:          Downloading itsdangerous-1.1.0-py2.py3-none-any.whl (16 kB)
remote:        Collecting Jinja2==2.11.2
remote:          Downloading Jinja2-2.11.2-py2.py3-none-any.whl (125 kB)
remote:        Collecting MarkupSafe==1.1.1
remote:          Downloading MarkupSafe-1.1.1-cp36-cp36m-manylinux1_x86_64.whl (27 kB)
remote:        Collecting Werkzeug==1.0.1
remote:          Downloading Werkzeug-1.0.1-py2.py3-none-any.whl (298 kB)
remote:        Installing collected packages: click, Werkzeug, itsdangerous, MarkupSafe, Jinja2, Flask
remote:        Successfully installed Flask-1.1.2 Jinja2-2.11.2 MarkupSafe-1.1.1 Werkzeug-1.0.1 click-7.1.2 itsdangerous-1.1.0
remote: -----> Discovering process types
remote:        Procfile declares types -> web
remote:
remote: -----> Compressing...
remote:        Done: 45.1M
remote: -----> Launching...
remote:        Released v3
remote:        https://flask-heroku-jalaz.herokuapp.com/ deployed to Heroku
remote:
remote: Verifying deploy... done.
To https://git.heroku.com/flask-heroku-jalaz.git
 * [new branch]      master -> master

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