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heroku

heroku recently added support for a process model which allows deployment of Pyramid applications.

This recipe assumes that you have a pyramid app setup using a Paste INI file, inside a package called ‘myapp’. This type of structure is found in the pyramid_starter scaffold, and other Paste scaffolds (previously called project templates). It can be easily modified to work with other Python web applications as well by changing the command to run the app as appropriate.

Step 0: Install heroku

Install the heroku gem per their instructions.

Step 1: Add files needed for heroku

You will need to add the following files with the contents as shown to the root of your project directory (the directory containing the setup.py).

requirements.txt:

You can autogenerate this file by running:

$ pip freeze > requirements.txt

You will have probably have a line in your requirements file that has your project name in it. It might look like either of the following two lines depending on how you setup your project. If either of these lines exist, delete them.

project-name=0.0
     or
-e git+git@xxxx:<git username>/xxxxx.git....#egg=project-name

Note

You can only use packages that can be installed from pypi. If you have any others that you checked out via git, or locally you will have to include these in your run file (see below). Never include these editable references when deploying to heroku.

Procfile:

Generate this by running:

$ echo "web: ./run" > Procfile

run:

Create run with the following:

#!/bin/bash
python setup.py develop
python runapp.py

Note

Make sure to chmod +x run before continuing. The ‘develop’ step is necessary because the current package must be installed before paste can load it from the INI file.

runapp.py:

If using a version of Pyramid prior to 1.3 (e.g. < 1.3), use the following for runapp.py:

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import os

from paste.deploy import loadapp
from paste import httpserver

if __name__ == "__main__":
    port = int(os.environ.get("PORT", 5000))
    app = loadapp('config:production.ini', relative_to='.')

    httpserver.serve(app, host='0.0.0.0', port=port)

Else if using a version greater or equal than 1.3 (e.g. >= 1.3), use the following for runapp.py:

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import os

from paste.deploy import loadapp
from waitress import serve

if __name__ == "__main__":
    port = int(os.environ.get("PORT", 5000))
    app = loadapp('config:production.ini', relative_to='.')

    serve(app, host='0.0.0.0', port=port)

Note

This assumes the INI file to use is production.ini, change as necessary. The server section of the INI will be ignored as the server needs to listen on the port supplied in the OS environ.

Step 2: Setup git repo and heroku app

Navigate to your project directory (directory with setup.py) if not already there. If you project is already under git version control, skip to the ‘Initialize the heroku stack’ section.

Inside your projects directory, if this project is not tracked under git it is recommended that you first create a good .gitignore file (you can skip this step). You can get the recommended python one by running:

$ wget -O .gitignore https://raw.github.com/github/gitignore/master/Python.gitignore

Once that is done, run:

$ git init
$ git add .
$ git commit -m "initial commit"

Step 3: Initialize the heroku stack

$ heroku create --stack cedar

Step 4: Deploy

To deploy a new version, push it to heroku:

$ git push heroku master

Make sure to start one worker:

$ heroku scale web=1

Check to see if your app is running

$ heroku ps

Take a look at the logs to debug any errors if necessary:

$ heroku logs -t

Tips & Tricks

The CherryPy WSGI server is fast, efficient, and multi-threaded to easily handle many requests at once. If you want to use it you can add cherrypy and pastescript to your setup.py:requires section (be sure to re-run pip freeze to update the requirements.txt file as explained above) and setup your runapp.py to look like:

example:

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import os

from paste.deploy import loadapp
from paste.script.cherrypy_server import cpwsgi_server

if __name__ == "__main__":
    port = int(os.environ.get("PORT", 5000))
    wsgi_app = loadapp('config:production.ini', relative_to='.')
    cpwsgi_server(wsgi_app, host='0.0.0.0', port=port,
                  numthreads=10, request_queue_size=200)

Heroku add-on’s generally communicate their settings via OS environ variables. These can be easily incorporated into your applications settings, for example:

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# In your pyramid apps main init
import os

from pyramid.config import Configurator
from myproject.resources import Root

def main(global_config, **settings):
    """ This function returns a Pyramid WSGI application.
    """

    # Look at the environment to get the memcache server settings
    memcache_server = os.environ.get('MEMCACHE_SERVERS')

    settings['beaker.cache.url'] = memcache_server
    config = Configurator(root_factory=Root, settings=settings)
    config.add_view('myproject.views.my_view',
                    context='myproject.resources.Root',
                    renderer='myproject:templates/mytemplate.pt')
    config.add_static_view('static', 'myproject:static')
    return config.make_wsgi_app()

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