Google App Engine

KalaPy is fully compatible with Google App Engine, including the Database Abstraction Layer. Actually, the Database Abstraction Layer resembles GAE datastore API in some extents, especially the Query interface.

However, following limitations have been imposed:

• No read/write access to file system.
• No transaction support.
• You can not perform queries with multiple inequality filters.

Getting started

You must have access to the Google App Engine Python SDK on your system. Download the SDK and extract the package somewhere and set an environment variable GAE_HOME pointing to the SDK directory. On Linux, do this:

$ export GAE_HOME=/path/to/google_appengine

KalaPy admin utility provides a gae command to perform various GAE related tasks. Apply ./admin.py gae -h command to see full help:

$ ./admin.py gae -h
Usage: admin.py gae <action> [options] [args]

Perform google appengine specific tasks.

Use the 'appcfg.py' and 'dev_appserver.py' (included in appengine sdk)
for other appengine specific tasks.

options:

  -a --address hostname for the appserver
  -p --port    port number for the appserver
  -i --install install libs (extra libs as arguments)
  -v --verbose enable verbose output
  -h --help    display help and exit

available actions:

  prepare    prepare this project for google appengine.
  rollback   launch 'appcfg.py rollback'
  runserver  launch 'dev_appserver.py runserver'
  update     launch 'appcfg.py update'

The first action you should perform is to prepare current project for GAE. This can be done with prepare action. Issue following command:

$ ./admin.py gae prepare

This will create app.yaml and gaehandler.py scripts in the project directory.

Configuration

The DATABASE_ENGINE configuration should be changed to "gae" and if you wish to use session, change the SESSION_ENGINE to either "db" or "memcached":

DATABASE_ENGINE = "gae"

...

SESSION_ENGINE = "memcached"

Also, make sure that the application name is properly set in app.yaml.

Run the development server

The gae admin command provides runserver action that will launch the dev_appserver that comes with the GAE SDK.

./admin.py gae runserver

Deploy the Application

Once your application is ready, you can deploy it on the App Engine. But before doing that, you have to prepare your application project to include all the thirdparty Python packages including KalaPy itself.

The prepare action of the gae command with -i option can be used to populate local lib directory with all the required Python packages/modules. You can also pass additional package names to the command line if you wish. For example, here is the command used to prepare the KalaPy example application:

$ ./admin.py gae prepare -i docutils roman

As the example application depends on docutils and roman modules. The KalaPy and other dependencies will be automatically installed in a local lib directory.

Now your application is ready to be deployed on GAE platform. Just issue following command:

$ ./admin.py gae update

You will be prompted for your GAE username and password. Once deployed, you can access your application from http://your-app.appspot.com/.

The included KalaPy example project has been deployed on GAE this way. You can access it here http://kalapy-demo.appspot.com/.