Quickstart for Python in the App Engine Flexible Environment

This quickstart shows you how to create a small App Engine application that displays a short message.

Before you begin

Before running and deploying this sample, take the following steps:

  1. Use the Cloud Platform Console to create a new Cloud Platform project, create an App Engine application, and enable billing:
    Go to App Engine

    When prompted, select the region where you want your App Engine application located and then enable billing.

  2. Install the following prerequisites locally:
    1. Download and install git.
    2. Download and install the Google Cloud SDK and then initialize the gcloud tool:
      Download the SDK
  3. Alternatively: You can use Google Cloud Shell, which comes with git and Cloud SDK already installed, and many other features, such as language support and code editors.

    After Google Cloud Shell is launched, you can proceed with the rest of this tutorial and execute your commands within Cloud Shell.

App Engine locations

App Engine is regional, which means the infrastructure that runs your apps is located in a specific region and is managed by Google to be redundantly available across all the zones within that region.

Meeting your latency, availability, or durability requirements are primary factors for selecting the region where your apps are run. You can generally select the region nearest to your app's users but you should consider the location of the other Cloud Platform products and services that are used by your app. Using services across multiple locations can affect your app's latency as well as pricing.

App Engine is available in the following regions:

  • us-central1
  • us-east1
  • us-east4
  • southamerica-east1 *
  • europe-west1
  • europe-west2
  • europe-west3
  • asia-northeast1
  • australia-southeast1

* For customers using the São Paulo region, all regional product SLAs will remain in force. However, multi-region and cross-region functionality spanning North America and South America may temporarily have reduced availability or performance.

You cannot change an app's region after you set it.

This quickstart demonstrates a simple Python application written with the Flask framework that can be deployed to App Engine. Although this sample uses Flask, you can use any framework that satisfies the requirements above. Alternative frameworks include Django, Pyramid, Bottle, web.py, Tornado, and more. To walk through a sample that uses Django, see Running Django in the App Engine Flexible Environment.

Download the Hello World app

We've created a simple Hello World app for Python so you can quickly get a feel for deploying an app to the App Engine flexible environment. Follow these steps from a command line to download Hello World to your local machine.

Download the sample app and navigate into the app directory:

  1. Clone the Hello World sample app repository to your local machine:

    git clone https://github.com/GoogleCloudPlatform/python-docs-samples
    

    Alternatively, you can download the sample as a zip file and extract it.

  2. Change to the directory that contains the sample code:

    cd python-docs-samples/appengine/flexible/hello_world
    

Run Hello World on your local machine

Mac OS / Linux

To run the Hello World app on your local computer:

  1. If you don't have virtualenv, install it using pip.

    sudo pip install virtualenv
    
  2. Create an isolated Python environment, and install dependencies:

    virtualenv env
    source env/bin/activate
    pip install -r requirements.txt
    
  3. Run the application:

    python main.py
    
  4. In your web browser, enter the following address:

    http://localhost:8080
    

Windows

If you have installed the Google Cloud SDK, you should already have Python 2.7 installed, typically in C:\python27_x64\ (for 64-bit systems). We'll be invoking the installation of Python packages by using Powershell.

  1. Install Powershell 3.0 or higher if you haven't already.

  2. Right-click on the shortcut to Powershell and start it as an Administrator.

  3. Try running the python command. If it's not found, add Python to your environment's PATH.

    $env:Path += ";C:\python27_x64\"
    
  4. Install the pip package manager for Python, and create an isolated Python environment with virtualenv, so that you aren't installing Hello World's dependencies system-wide in the next step.

    iwr https://bootstrap.pypa.io/get-pip.py -OutFile get-pip.py
    python get-pip.py
    python -m pip install virtualenv
    python -m virtualenv env
    
  5. Activate your isolated Python environment by granting signed downloaded scripts permission to run, and install Hello World's requirements.

    Set-ExecutionPolicy RemoteSigned
    .\env\Scripts\activate
    python -m pip install -r requirements.txt
    
  6. Finally, run the application and view Hello World at http://localhost:8080.

    python main.py
    

You can see the Hello World message from the sample app displayed in the page.

In your terminal window, press Ctrl+C to exit the web server.

Deploy and run Hello World on App Engine

To deploy your app to the App Engine flexible environment:

  1. Deploy the Hello World app by running the following command from the hello_world directory:
    gcloud app deploy
    Learn about the optional flags.

    Common gcloud command flags

    • Include the --version flag to specify an ID that uniquely identifies that version of your app, otherwise one is generated for you. Example: --version [YOUR_VERSION_ID]
    • Include the --project flag to specify an alternate Cloud Platform project ID to what you initialized as the default in the gcloud tool. Example: --project [YOUR_PROJECT_ID]

    Example:

    gcloud app deploy --version pre-prod-5 --project my-sample-app

    To learn more about deploying your app from the command line, see Testing and Deploying Your App . For a list of all the command flags, see the gcloud app deploy reference.

  2. Launch your browser and view the app at http://YOUR_PROJECT_ID.appspot.com, by running the following command:
    gcloud app browse
This time, the page that displays the Hello World message is delivered by a web server running on an App Engine instance.

Congratulations! You've deployed your first Python app to App Engine flexible environment!

See the following sections for information about cleaning up as well as links to the possible next steps that you can take.

Clean up

To avoid incurring charges, you can delete your Cloud Platform project to stop billing for all the resources used within that project.

  1. In the Cloud Platform Console, go to the Projects page.

    Go to the Projects page

  2. In the project list, select the project you want to delete and click Delete project. After selecting the checkbox next to the project name, click
      Delete project
  3. In the dialog, type the project ID, and then click Shut down to delete the project.

What's next

Learn the whole platform

Now that you know what it's like to develop and deploy App Engine apps, you can stretch out and see the rest of Google Cloud Platform. You already have the Google Cloud SDK installed and that gives you the tools to interact with products like Google Cloud SQL, Google Cloud Storage, Google Cloud Datastore, and more. For a guided walkthrough that teaches you how to create an application that uses the entire platform, not just App Engine, check out our quickstart on creating the Bookshelf app.

Learn about the App Engine flexible environment

Here are some topics to help continue your learning about App Engine.

Hello World code review

Hello World is the simplest possible App Engine app, as it contains only one service, has only one version, and all of the code is located within the app's root directory. This section describes each of the app files in detail.

main.py

The Hello World app is a very basic one-file Flask application.

import logging

from flask import Flask


app = Flask(__name__)


@app.route('/')
def hello():
    """Return a friendly HTTP greeting."""
    return 'Hello World!'


@app.errorhandler(500)
def server_error(e):
    logging.exception('An error occurred during a request.')
    return """
    An internal error occurred: <pre>{}</pre>
    See logs for full stacktrace.
    """.format(e), 500


if __name__ == '__main__':
    # This is used when running locally. Gunicorn is used to run the
    # application on Google App Engine. See entrypoint in app.yaml.
    app.run(host='127.0.0.1', port=8080, debug=True)

app.yaml

The app.yaml file describes an application's deployment configuration:

runtime: python
env: flex
entrypoint: gunicorn -b :$PORT main:app

runtime_config:
  python_version: 3

Here, app.yaml specifies the runtime used by the app, and sets env: flex, specifying that the app uses the flexible environment.

The entrypoint tells App Engine how to start the app. This app uses gunicorn to serve the Python application. The $PORT variable is set by App Engine when it starts the app. For more information about entrypoint, see Application Startup.

Additionally, the optional runtime_config section sets python_version to use Python 3. If python_version is not specified, then Python 2 is used by default. You can also specify python_version: 2 explicitly.

requirements.txt

requirements.txt and the Python package manager pip are used to declare and install application dependencies. Hello World requires Flask, a web framework, and Gunicorn, a WSGI server.

Flask==0.12.2
gunicorn==19.7.1

requirements.txt defines the libraries that will be installed both locally and when deploying to App Engine.

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App Engine flexible environment for Python docs