Python¶

Python with the Legacy Buildpack¶

If your Python application is configured for running on Helion Stackato 2.10 or earlier, you can deploy it using the Legacy Buildpack, which provides an updated version of the old Python framework.

With the Legacy Buildpack, applications are run with uWSGI. Applications are started from a top-level script called wsgi.py defining a global application variable containing the WSGI application object. For a minimal sample application, see wsgi-helloworld.

You may add additional arguments to uWSGI in your manifest.yml. For example:

processes:
  web: $STACKATO_UWSGI --mount foo=app.py --import module

It is possible to serve static files with uWSGI.

Django¶

Application URL¶

Some applications require the user to specify the APP_URL. The following example obtains the correct urls:

import json
vcap_app = json.loads(os.environ['VCAP_APPLICATION'])
APP_URL = 'http://' + vcap_app['uris'][0]

Database Services¶

Some minor edits are required to make your application work with a database. Python database configurations are located inside settings.py.

import urlparse
DATABASES = {}
if 'DATABASE_URL' in os.environ:
    url = urlparse.urlparse(os.environ['DATABASE_URL'])
    DATABASES['default'] = {
        'NAME': url.path[1:],
        'USER': url.username,
        'PASSWORD': url.password,
        'HOST': url.hostname,
        'PORT': url.port,
        }
    if url.scheme == 'postgres':
        DATABASES['default']['ENGINE'] = 'django.db.backends.postgresql_psycopg2'
    elif url.scheme == 'mysql':
        DATABASES['default']['ENGINE'] = 'django.db.backends.mysql'
else:
    DATABASES['default'] = {
        'ENGINE': 'django.db.backends.sqlite3', # Add 'postgresql_psycopg2', 'postgresql', 'mysql', 'sqlite3' or 'oracle'.
        'NAME': 'dev.db',                      # Or path to database file if using sqlite3.
        'USER': '',                      # Not used with sqlite3.
        'PASSWORD': '',                  # Not used with sqlite3.
        'HOST': '',                      # Set to empty string for localhost. Not used with sqlite3.
        'PORT': '',                      # Set to empty string for default. Not used with sqlite3.
        }

import json
vcap_services = json.loads(os.environ['VCAP_SERVICES'])
srv = vcap_services['mysql'][0]
cred = srv['credentials']
DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': cred['name'],
        'USER': cred['user'],
        'PASSWORD': cred['password'],
        'HOST': cred['hostname'],
        'PORT': cred['port'],
    }
}

Worker Applications¶

Non-HTTP apps that run as a Helion Stackato application under the control of the Health Manager.

To deploy worker applications, you need to use the command: key and set the processes: web: key to Null (~).

name: python-app
framework:
  type: python
  runtime: python27
command: python worker.py
processes:
  web: ~

Serving Static Files with uWSGI¶

It is possible to serve static files with uWSGI using processes: web: in the manifest.yml file to specify directories that will be served statically and not by the app.

To make a single directory serve statically, use --check-static:

processes:
  web: $STACKATO_UWSGI --check-static $HOME/<directory>

To specify multiple directories with static files that do not share a common root, use --static-map:

processes:
  web: $STACKATO_UWSGI --static-map /foo=$HOME/static --static-map /bar=$HOME/sub

In this case /foo/index.html would serve $HOME/static/index.html, and /bar/index.html would serve $HOME/sub/index.html. If the file does not exist, then uWSGI will forward the request to the app.

Using a custom web server¶

To use a different web server, instead of uWSGI, specify its startup command in manifest.yml. Here's a sample manifest.yml used to deploy a Django 1.4 application named dj14 using gunicorn:

name: dj14

framework:
  type: python

processes:
  web: gunicorn -b 0.0.0.0:$PORT dj14.wsgi

requirements:
  pypm: [gunicorn]
  pip: ["http://www.djangoproject.com/download/1.4-beta-1/tarball/#egg=django-1.4b1"]

The custom web server must bind to IP address 0.0.0.0 and port $PORT. The same trick can be used to serve non-WSGI applications (such as Tornado). See the bottle-py3 example sample for an example.

Installing Python Packages¶

Application dependencies such as web frameworks or modules from PyPI can be installed using PyPM and/or pip.

requirements:
  pypm:
    - tornado
    - pymongo

requirements:
  pypm:
    - tornado
    - pymongo
  pip:
    - pycurl

PyPy Support¶

Here is an example of pushing an app using PyPy.

First, clone the https://github.com/Stackato-Apps/werkzeug-debugger repository.

Then add a buildpack: entry to the manifest.yml file:

buildpack: git://github.com/mtigas/heroku-buildpack-pypy.git

Finally, push the app to Helion Stackato:

$ stackato push -n

Other Python Frameworks¶

Examples of deploying other frameworks are included in the GitHub samples repo:

• Bottle Framework
  • Bottle Currency
  • Python 3
• Django
  • django-gtd
  • pinax-social
• Pylons Pyramid
  • virginia
  • default
• Tornado
  • chat
• Werkzeug
  • werkzeug-debugger
• Celery
  • celery-demo