Overview
--------

Silk is a Fabric_ based tool for setting up Python WSGI apps on what I like to
call the SNUG stack:

* Supervisord_ for starting processes and keeping them alive.
* Nginx_ for proxying between your WSGI app and the big bad web.
* Ubuntu_ as the OS of choice, enabling resolution of system dependencies with
  apt.  Debian might work as well but hasn't been tested.
* Gunicorn_ for serving your WSGI app.

(I suppose it could also be the GUNS stack but that sounds far less friendly.)

Key Features
~~~~~~~~~~~~

* Deploy your site to one or more servers with a single command ('silk push').
* Automatic configuration of Nginx, Supervisord, and Gunicorn to get your site running.
* Isolation of each site into a separate Virtualenv_
* Support for differing app config depending on which role you deploy to (a 
  different DB in staging than production, for example).

Installation
~~~~~~~~~~~~

Use pip::

    pip install silk-deployment

You can also install the current development version straight from bitbucket::

    pip install hg+http://bits.btubbs.com/silk-deployment#egg=silk-deployment

Commands
--------

(Almost) all of the commands below require that you specify a role name, like
'silk dosomething -R dev'.

Commands can generally be run from the site root directory or any subdirectory
of it.

push
~~~~

::

    silk push -R rolename

This command is the main reason for Silk's existence. It does the work required
to get your app running on a host (or set of hosts) given the configuration
specified in site.yaml and the selected role .yaml file.  'push' does the
following:

1. SSHes to the remote server(s) specified in the role config.
2. Copies the site from your local machine to a temporary directory on the
   remote server.
3. Creates a virtualenv for the site.
4. Installs python dependencies into the virtualenv.
5. Writes config file includes for nginx and supervisord.
6. Writes a supervisord config for the site and starts it up.
7. Makes a request to the homepage to ensure the site is running.
8. Tells nginx to route traffic to the new instance instead of the old one.

run
~~~

::

    silk run -R rolename

This command runs the site from the local machine, on port 8000.  (Nothing is
pushed of copied.)  Static directories listed in the *static_dirs* section of
site.yaml will also be served.  (CherryPy is used for this magic.)

skel
~~~~

::

    silk skel sitename

Creates a directory with a basic Silk file and directory structure.

Layout
------

A silk-enabled project should be layed out something like this::

  mysite.com
  ├── fabfile.py
  ├── membrane.py
  ├── requirements.txt 
  ├── roles
  │   ├── dev.yaml
  │   ├── staging.yaml
  │   └── production.yaml
  ├── site.yaml
  └── my-django-project

Some of those files/folders are required, other are optional:

Required
~~~~~~~~

1. site.yaml - This is the main config file (comparable to app.yaml in Google
   App Engine)
2. requirements.txt - A pip-compatible list of Python package names and
   versions.
3. roles/\*.yaml - One or more 'role' files that contain the config to be 
   passed into your app depending on the deployment context.

All of the required files will be created for you with the 'silk skel' command.

Optional
~~~~~~~~

1. membrane.py - For Django projects it's nice to have a little shim to expose
   the project as a WSGI app.  I like to call mine membrane.py.  You can use 
   whatever you like, or nothing at all, depending on your setup.
2. my-django-project - Silk isn't restricted to Django; any valid WSGI app on 
   your Python path should be servable.  But for Django projects I think it 
   makes sense to stick them right there.
3. fabfile.py - A Fabric_-compatible fabfile that imports Silk's Fabric 
   functions.  This is where you can customize Silk's 'push' function by
   wrapping it with your own (I do this to run Django's "collectstatic" on
   push), or add in your own Fabric tasks.

.. _Supervisord: http://supervisord.org/
.. _Nginx: http://nginx.org/
.. _Ubuntu: http://www.ubuntu.com/
.. _Gunicorn: http://gunicorn.org/
.. _Fabric: http://docs.fabfile.org/
.. _Virtualenv: http://virtualenv.openplans.org/
