py-holder

Tools for developing python Flask apps in public Cloud

Basic placeholder python app

This project is a basic Python Flask web application template to use as blueprint for new projects or as a basic placeholder for different kinds of environments and CI/CD procedures, focused on backend development and environment troubleshooting procedures.

Apart from the python code, basic templates for Docker, Kubernetes, Google GKE, Cloud Run environments and CI/CD systems like Jenkins, GitHub Actions, Google Cloud Build, Google Cloud Deploy are to be provided during the project lifetime, to compare Compute environments and CI/CD solutions procedures.

The python application

It implements a light JSON web application built with Flask with several useful endpoints when developing in a Cloud environment.
The list is constantly under revision. For now, these endpoints are implemented:

Endpoints

/              returns HTTP code 200 + json payload with app info

/healthcheck   returns HTTP code 200 + json payload with status info

/ctime         returns HTTP code 200 + json payload with current time info

/mirror        returns HTTP code 200 + json with info about the incoming request processed, including cookies

/redirect      returns HTTP code 302 and sets location to root path

/stamp         returns HTTP code 200 and sets response cookie (key and value from app configuration)

App configuration keys used

# App name for HTML views, it appears on titles, links, etc.
VIEW_APP_NAME = os.environ.get('VIEW_APP_NAME') or 'py-holder-demo'

# App info
APP_NAME = os.environ.get('APP_NAME') or 'py-holder-demo'
APP_VER = os.environ.get('APP_VER') or '1.0'

# Cookie settings for /stamp endpoint
STAMP_COOKIE_KEY = os.environ.get('STAMP_COOKIE_KEY') or 'x-stamp'
STAMP_COOKIE_VALUE = os.environ.get('STAMP_COOKIE_VALUE') or base64.urlsafe_b64encode(APP_NAME.encode())

Running the application locally

Use Google Cloud Shell

• Create a Google Cloud platform account if you do not already have it.
• Create a Google Cloud project or use an existing one.
• To start coding right away, launch Google Cloud Shell.

...or use your own development environment

Requirements

• Install python packages.

  sudo apt update
  sudo apt install python3 python3-dev python3-venv

• Install pip

  Note: Debian provides a package for pip

  sudo apt install python-pip

  Alternatively pip can be installed with the following method

  wget https://bootstrap.pypa.io/get-pip.py
  sudo python3 get-pip.py

Note: Console snippets for Debian/Ubuntu based distributions.

Clone git repo from Github

At this point either you are using Cloud Shell or you have a local development environment with python and Cloud SDK.

git clone https://github.com/amesones-dev/py-holder.git

Create a pyhon virtual environment

User your cloned git repository folder for your source code and Python venv virtual environment to isolate python dependencies.

cd py-holder
python -m venv [venv-name]
source [venv-name]/bin/activate

Usual values for [venv-name] are venv, dvenv, venv39 for a python 3.9 version virtual environment, etc.

Install python requirements

# From py-holder/src folder
pip install -r requirements.txt

App configuration

At this point you are ready to configure and run the application.

Running the app

• Set Flask environment variables

export  FLASK_SECRET_KEY=$(openssl rand -base64 128)
export  FLASK_APP=app:create_app

• Run with flask

flask run   

• Or run with gunicorn

gunicorn start:app   

Use example

# HTTP 
export ENDPOINT='healthcheck'
curl  "http://localhost:${PORT}/${ENDPOINT}"

# HTTPS 
curl  "https://localhost:${PORT}/${ENDPOINT}"

# HTTPS self-signed  certificate
curl --insecure "https://localhost:${PORT}/${ENDPOINT}"


# Basic app endpoints tests
curl -s  localhost:${PORT} |jq
{
  "name": "py-holder-APP-demo",
  "ver": "1.0"
}
curl -s  localhost:${PORT}/healthcheck |jq
{
  "status": "OK"
}
curl -s  localhost:${PORT}/ctime |jq
{
  "now_utc_iso": "2023-09-01T13:59:25.691353",
  "now_utc_timestamp": "1693576765.691366",
  "status": "OK"
}
curl -s  localhost:${PORT}/mirror |jq
{
  "0_id": "8784090160585",
  "1_server": [
    "0.0.0.0",
    5000
  ],
  "2_path": "/mirror",
  "3_method": "GET",
  "5_headers": {
    "Accept": "*/*",
    "Host": "localhost:8080",
    "User-Agent": "curl/7.74.0"
  },
  "6_cookies": {}
}

# Ask curl to use cookies and capture them to file
curl -s  -c capture_cookies localhost:${PORT}/stamp |jq
{
  "status": "OK"
}

cat capture_cookies 
# Output
# ...
# localhost       FALSE   /       FALSE   0       x-stamp KCcwLjAuMC4wJywgNTAwMCk=


# Use curl captured cookies from file with cookies
# Notice how the mirror endpoint now receives the cookie sent by curl
curl -s  -b capture_cookies localhost:${PORT}/mirror |jq
{
  "0_id": "8784090161032",
  "1_server": [
    "0.0.0.0",
    5000
  ],
  "2_path": "/mirror",
  "3_method": "GET",
  "5_headers": {
    "Accept": "*/*",
    "Cookie": "x-stamp=KCcwLjAuMC4wJywgNTAwMCk=",
    "Host": "localhost:8080",
    "User-Agent": "curl/7.74.0"
  },
  "6_cookies": {
    "x-stamp": "KCcwLjAuMC4wJywgNTAwMCk="
  }
}

# Non existent endpoint
export ENDPOINT=app_does_not_implement
curl -I -s  localhost:${PORT}/${ENDPOINT} --output http-test-${ENDPOINT}.log 
grep   'HTTP' http-test-${ENDPOINT}.log
# Output
  HTTP/1.1 404 NOT FOUND