Installing Flask on Linux or Mac

On Debian 10 or Ubuntu 20:

sudo pip3 install flask flask-cors

On Mac or FreeBSD:

sudo pip install flask flask-cors

Creating a basic flask app:

#!/usr/bin/env python3

from flask import Flask, request, jsonify

app = Flask(__name__)

@app.route("/", defaults = {'path': ""})
@app.route("/<string:path>")
@app.route("/<path:path>")

def index(path):
    req_info = {
        'host': request.host.split(':')[0],
        'path': "/" + path,
        'query_string': request.args,
        'remote_addr': request.environ.get('HTTP_X_REAL_IP', request.remote_addr),
        'user_agent': request.user_agent.string
    }
    return jsonify(req_info)

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

Run the app

chmod u+x main.py
./main.py
Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

Do a test curl against it

$ curl -v "http://localhost:5000/oh/snap?x=1&x=2"

< HTTP/1.0 200 OK
< Content-Type: application/json
< Content-Length: 65
< Access-Control-Allow-Origin: *
< Server: Werkzeug/1.0.1 Python/3.7.8
< Date: Wed, 21 Apr 2021 17:07:58 GMT
<
{"host":"localhost","path":"/oh/snap","query_string":{"x":"1"},"remote_addr":"127.0.0.1","user_agent":"curl/7.72.0"}

Deploying to Google Cloud App Engine

Create a requirements.txt file:

echo "flask" > requirements.txt

Create an app.yaml file:

printf "runtime: python38\nenv: standard\n" > app.yaml 

Now deploy the app to Google using the gCloud command:

gcloud app deploy