van.static 1.8

Workflow

This tool aids in implementing a very specific workflow using static files and pyramid:

• During development static files are stored in subversion and are configured as normal in Pyramid applications.

• Before deployment, the static files are extracted from the eggs by the system administrator and uploaded to a CDN. The URL on the CDN varies depending on the egg version the files where extracted from.

• During extraction, CSS and JS files can be optionally minified.

• In production, the system administrator configures the application to use static files from the CDN.

This workflow has these advantages:

• Minimal impact on development. Changes to files are immediately visible, also developers work with un-compressed files.

• CDN served files can have very long cache-control times while still allowing them to be updated almost immediately on application upgrade.

Testing an extraction

You can try out the extract tool by running the cdn.py file directly. The following commands will extract the static resource from the deform package to the test_extract directory:

$ mkdir test_extract $ python van/static/cdn.py –target “file://$(pwd)/test_extract” –resource deform:static

NOTE: the deform package must be on the python path.

If you use a url like this s3://mybucket/path/to/files/ the extracted resources will be placed directly in Amazon S3. You need to manually install boto to be able to use this functionality.

Implementing in your application

One way would be to have code like this in your package:

>>> def my_extract_filesystem_command():
...     """Customized extract command for my application"""
...     cdn.extract_cmd(['myapp:static', 'deform:static'], yui_compressor=True)

>>> from pyramid.config import Configurator
>>> def make_pyramid_app(cdn_url=None):
...     config = Configurator()
...     config.include('van.static.cdn')
...     config.add_cdn_view(cdn_url or 'myapp_static', 'myapp:static')
...     config.add_cdn_view(cdn_url or 'deform_static', 'deform:static')
...     return config.make_wsgi_app()

You would make my_extract_filesystem_command a command line script for the system administrator to run on deployment. Likewise the cdn_url configuration option is set by the system administrator to the url where the files were exported to.

GZip Content-Encoding compression

Compressing resources during extraction is supported for the S3 target. S3 and Cloudfront does not directly support on the fly compression at this time so a workaround is used where multiple copies of resources are uploaded. One without any encoding and the others with encodings.

The links to resources should then be generated to compressed or non-compressed resources depending on the capabilities of the browser.

An example of how to modify the resource generation in a pyramid application is:

>>> from pyramid.request import Request
>>> class ZippingPyramidRequest(Request):
...
...     def static_url(self, path, **kw):
...         if 'gzip' in self.accept_encoding:
...             package, path = path.split(':', 1)
...             path = '{package}:gzip/{path}'.format(
...                     package=package,
...                     path=path)
...         return Request.static_url(self, path, **kw)

The extractor is configured to upload resources with the gzip encoding with the –encoding parameter.

WARNING: The Vary HTTP will need to contain Accept-Encoding to play well with any caches.

APT integration

For system administrators who use APT to install packages, a useful trick is put a snippet into /etc/apt/apt.conf.d/:

DPkg::Post-Invoke::      "/path/to/extraction/script";

So that the extraction script runs whenever packages are installed on the application servers. Note that if you have etckeeper installed, this should be placed afterwards.