Running Flask App with HttpPlatformHandler in Azure App Services(Windows)

3 minute read | By Prashanth Madi

Flask is a micro web framework written in Python and based on the Werkzeug toolkit and Jinja2 template engine.

Below are list of steps we would follow

  • Create Sample Project
  • Create Azure WebApp and Use Site Extension to Upgrade Python
  • Create and Change Deployment script
  • Adding web.config (for production app with waitress)
  • Publish App

You can find a Sample Python Flask project with above operations @ GitHub Link

Create Sample Project in local environment

  • Create index.py file with below content

    from flask import Flask
    app = Flask(name)

    @app.route(“/”) def hello():
    return “Hello World!”

    if name == “main”:
    app.run()

  • Create requirements.txt file with below content

    Flask==0.12

  • Install dependencies listed in requirements.txt file using below command.

    pip install –upgrade -r requirements.txt

  • Run app in local environment using below command

    $ python index.py

    • Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

  • Navigate to http://127.0.0.1:5000/ and you should see app up and running

Create Azure WebApp and Use Site Extension to Upgrade Python

Navigate to Azure portal

  • Create a new web app
  • Setup Continuous Deployment
  • Navigate to your App Service blade, select Extensions and then Add.
  • From the list of extensions, scroll down until you spot the Python logos, then choose the version you need

For this blog I’m choosing Python 2.7.12 x64, It would install new version of python @ D:\home\Python27 If you choose Python 3.5.2 x64, It would install new version of python @ D:\home\Python35

Create and Change Deployment script

I have explained more on how to utilize deployment script and what it does @ link. you can use this script to run commands on Azure App Services after moving code to it. Install Azure Cli using below command

npm install azure-cli -g

Use Below command to create deployment script.

azure site deploymentscript --python

Above step would create below two files

  • .deployment
  • deploy.cmd

Note: If you haven’t used nodejs/npm earlier, Create above files manually and copy content for these files from https://github.com/prashanthmadi/azure-flask-httpplatformhandler Replace content of deploy.cmd file with content at Link We are changing default deployment script(removing virtual environment creation and others) and adding below content to install packages listed in requirements.txt

:: 2. Install packages
echo Pip install requirements.  
D:\home\Python27\python.exe -m pip install --upgrade -r requirements.txt  
IF !ERRORLEVEL! NEQ 0 goto error

If you are using Python35 site extension change path from D:\home\Python27\python.exe to D:\home\Python35\python.exe in deploy.sh

D:\home\Python35\python.exe -m pip install --upgrade -r requirements.txt

Adding web.config(Production Mode - Using Waitress)

Waitress is meant to be a production-quality pure-Python WSGI server with very acceptable performance Create web.config file with below content

<?xml version="1.0" encoding="UTF-8"?>  
<configuration>  
 <system.webServer>
  <handlers>
   <add name="httpPlatformHandler" path="*" verb="*" 
         modules="httpPlatformHandler" resourceType="Unspecified" />
  </handlers>

  <httpPlatform processPath="D:\home\Python27\python.exe"
 arguments="run_waitress_server.py" requestTimeout="00:04:00" startupTimeLimit="120" startupRetryCount="3" stdoutLogEnabled="true">
   <environmentVariables>
    <environmentVariable name="PYTHONPATH" value="D:\home\site\wwwroot" />
    <environmentVariable name="PORT" value="%HTTP_PLATFORM_PORT%" />
   </environmentVariables>
  </httpPlatform>
 </system.webServer>
</configuration>

If you observe carefully, we have

  • httpplatform arguments section to run run_waitress_server.py file
  • Added new evnironmentVariable PORT to pass the internal port number we use in waitress

If you use Python35 site extension, change web.config content to use D:\home\Python35\python.exe for processPath

 <httpPlatform processPath="D:\home\Python35\python.exe"
 arguments="run_waitress_server.py" requestTimeout="00:04:00" startupTimeLimit="120" startupRetryCount="3" stdoutLogEnabled="true">

Add below line at the end in requirements.txt file. This would install waitress module during deployment

waitress==1.0.1

Create a new file run_waitress_server.py with below content

import os  
from waitress import serve  
from index import app

serve(app,host="0.0.0.0",port=os.environ["PORT"])

Publish App

Navigate to your root folder and commit your changes to WEB_APP_GIT_URL

git init  
git add .  
git commit -m "initial commit"  
git remote add sampleflaskapp WEB_APP_GIT_URL  
git push sampleflaskapp master

You can find a Sample Python Flask project with above operations @ GitHub Link

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