Minimal Flask app on Google App Engine

Feeling overwhelmed by all Google Cloud Platform documentation? Have no fear. Here is how to create and deploy the simplest possible Flask app running on Google App Engine standard environment in three easy steps.

Step 1 - Setup Google Cloud Platform

First make sure that you have a working installation of Python 2 and pip. Install Google Cloud SDK on your computer and register for the Google Cloud Platform Free Trial. Before proceeding to Step 2 make sure that gcloud and dev_appserver.py commands are available on the command line.

Step 2 - Write the app

Create some boilerplate first.

# create a folder to host the app
$ mkdir simple && cd simple

# add Flask to the requirements file
$ echo Flask==0.12.1 > requirements.txt

# install the requirements
$ pip install -t lib -r requirements.txt

Create main.py file with the following contents.

from flask import Flask

app = Flask(__name__)

@app.route('/')
def index():
    return 'hello google app engine!'

Create appengine_config.py with the following contents. Needed for external dependencies.

from google.appengine.ext import vendor

vendor.add('lib')

Finally add app.yaml which is the configuration file.

runtime: python27
api_version: 1
threadsafe: true

handlers:
- url: /.*
  script: main.app

Test run the app locally.

$ dev_appserver.py .

You should now be able to access it.

$ curl localhost:8080

Step 3 - Deploy the app

Lets now deploy the app and see it run live in the cloud.

# login to be able to deploy the app
$ gcloud auth login

# create new GCP project (change name here)
$ export PROJECT_ID=simple-gae-project-2134
$ gcloud projects create $PROJECT_ID

# set this project to current project
$ gcloud config set project $PROJECT_ID

# check your config
$ gcloud config list

# you need to create the app first in the specific region.
# omit the region to choose it interactivelly.
$ gcloud app create --region=us-east1

# now deploy the code
$ gcloud app deploy

# open app in the browser
$ gcloud app browse

Done. That’s all there is to it.