Heroku

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

This recipe assumes that you have a Pyramid application 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 application 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 with the following command.

$ pip freeze > requirements.txt

In your requirements.txt file, you will probably have a line with your project's 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

注釈

You can only use packages that can be installed with pip (e.g., those on PyPI, those in a git repo, using a git+git:// url, etc.). If you have any that you need to install in some special way, you will have to do that in your run file (see below). Also note that this will be done for every instance startup, so it needs to complete quickly to avoid being killed by Heroku (there's a 60-second instance startup timeout). Never include editable references when deploying to Heroku.

Procfile

Generate Procfile with the following command.

$ echo "web: ./run" > Procfile

run

Create run with the following command.

#!/bin/bash
set -e
python setup.py develop
python runapp.py

注釈

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 greater than or equal to 1.3 (e.g. >= 1.3), use the following for runapp.py.

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)

For versions of Pyramid prior to 1.3 (e.g. < 1.3), use the following for runapp.py.

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)

注釈

We assume the INI file to use is named production.ini, so change the content of runapp.py as necessary. The server section of the INI will be ignored as the server needs to listen on the port supplied in the OS environment.

Step 2: Setup git repo and Heroku app

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

Inside your project's directory, if this project is not tracked under git, it is recommended yet optional to create a good .gitignore file. You can get the recommended python one by running the following command.

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

Once that is done, run the following command.

$ 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 and 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 cherrpy 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 the following.

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-ons generally communicate their settings via OS environment variables. These can be easily incorporated into your applications settings as show in the following example.

# 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()