A recipe for App Engine

Gabi de Maeztu http://merqur.io

Target

The [ideal] solution

• Easy
• Fast to build
• Free or almost
• No maintenance

What is flask

• Flask is a web microframework
• Based on Werkzeug (WSGI), Jinja 2
• It's BSD licensed

Why flask

• Nobody* has time to properly test the framework and read the code
• Learn as you go *Almost

flask is simple

						
from flask import Flask

app = Flask(__name__)

@app.route("/")
@app.route("/home/")
def hello():
	return "Hello World!"

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

That easy

What flask does

• Built in dev server and debugger
• Routing
• Template rendering
• Access request data
• Manage sessions
• [ . . . ]

What flask doesn't

• Automated admin interface
• Authentication
• l10n / i18n
• Syndication feeds (RSS/Atom)
• Sitemaps
• It's not Django (❤) Nor intends.

How does it work

HTTP & WWW

HTTP Request

HTTP Response

MVC

• M ⇒ "Model"
• V ⇒ View
• C ⇒ Controller

MVC [1]

MVC [2]

MVC [3]

Views [1]

• Whatever you want to return
• Text
• HTML, JSON
• Other crazy stuff [. . .]

Views [2]

Views [3]

						
from flask import render_template

@app.route('/hello/')
@app.route('/hello/< name>')
def hello(name=None):
	return render_template('hello.html', name=name)
						
					

Views [4]

						

Hello from Flask
{% if name %}

Hello {{ name }}!

Hello World!

Easy to setup

						
$ pip install flask
						
					

Even nicer if we use virtualenv, so our libraries do not mess up

						
$ mkdir flask

$ virtualenv flask/
	New python executable in flask/bin/python3.4
	Also creating executable in flask/bin/python
	Installing setuptools, pip, wheel...done.

$ . flask/bin/activate
(flask)$ cd flask/
(flask)$ pip install flask
						
					

now what ?

• Create an app.py file
• Start a Flask instance

						
# import the framework
from flask import Flask

# create an instance
app = Flask(__name__)

# define a route and a 'controller'
@app.route("/")
def hello():
	return "Hello World!"

# if runing this script, start up dev server
if __name__ == "__main__":
	app.run()
						
					

Run it

						
$ python hello.py
	* Running on http://localhost:8000/
						
					

Let's build a rocket

What is it ?

• PASS | Platform as a Service
• Java, Python, Go, PHP
• Python 2.7.3
• Replicated over the Google servers
• Resources depend on need ⇒ Flexible billing

Pros

• Scalable
• Easy and cheap
• Nice option for start-ups/individuals
• Zero maintenaince
• Lot of APIs (Email, Image, DB [. . .])
• Free quota per day1 GB Traffic,50k read/write to DB, 5GB Store

Cons

• Not for CPU intensive apps
• Can't use libraries with non python code
• No multithreading
• Locked to App Engine ? (AppScale)
• Not an easy filesystem

Workflow

GAE Installation

						
$ curl https://sdk.cloud.google.com | bash

or

$ docker pull google/cloud-sdk
						
					

Flask ❤ App Engine

Using GAE skeleton

• In a Git repository (link)
• Adds libraries in /lib to path
• Libraries in /lib will be uploaded

Let's start a project

						
$ git clone https://github.com/GoogleCloudPlatform/appengine-python-flask-skeleton

$ cd appengine-python-flask-skeleton

$ pip install -r requirements.txt -t lib
						
					

Let's start a project [2]

Configuration file

						
application: flask-pybcn #your app id here
version: 1
runtime: python27
api_version: 1
threadsafe: yes

- url: .* # This regex directs all routes to main.app
	script: main.app

						
					

main.py

						
# Import the Flask Framework
from flask import Flask
app = Flask(__name__)

# We don't need to call run() since our application is embedded within
# the App Engine WSGI application server.

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

Run locally or Deploy

						
$ dev_appserver.py .  # Run's a server at localhost:8080

$ appcfg.py -A project-id update . # Deploy to App Engine
						
					

Deployment

Available at project-id.appspot.com

Flask on esteroids

NDB Datastore

						
from google.appengine.ext import ndb

class Publication(ndb.Model):
    """A publication object."""
    date = ndb.DateTimeProperty(auto_now_add=True)
    title = ndb.StringProperty(required=True)
    pages = ndb.IntProperty()
    year = ndb.DateTimeProperty()
    is_book = ndb.BooleanProperty()
						
					

NDB Datastore [2]

						
little_prince = Publication(title='The Little Prince')
little_prince.pages = 112
little_prince.year = datetime.date(1943, 04, 06)
little_prince.is_book = True

little_prince.put()
						
					

NDB Datastore [3]

Creating an Interface

Creating an Interface [2]

						
@app.route('/')
def index():
    return render_template('index.html')

						
					

Creating an Interface [3]

						
from models import Publication

@app.route('/', methods=['GET', 'POST'])
def index():
	if request.method == 'POST':

		little_prince = Publication()
		little_prince.title = request.form['title']

		little_prince.put()

	return render_template('index.html')

						
					

Creating an Interface [4]

						
@app.route('/', methods=['GET', 'POST'])
def index():
  if request.method == 'POST':
    little_prince = Publication()
    little_prince.title = request.form['title']

	little_prince.put()

  all_pub = Publication.query().fetch()

  return render_template('index.html', pubs=all_pub)

						
					

Creating an Interface

Jinja templating

						
{% for publication in pubs %}
	

{{ publication.title }}

Rocket Science 101

Real world examples