Using Feature Flags with Sculpin
Background
I was asked last week to add a new feature, a Facebook pixel for measuring and building advertising campaigns, to a client's website which I built using the Sculpin static site generator.
The site uses settings within the app/config/sculpin_site.yml file for
storing site IDs and usernames. For this, I would add something like:
facebook:
pixel:
id: "abc123"
It can then be retrieved with .
If I then needed to disable the pixel, then I'd typically remove the pixel ID:
facebook:
pixel:
id: ~
Introducing feature flags
A technique that I like to use on other projects is using feature flags (aka feature toggles).
Whilst, in this instance, a feature flag wouldn't separate deploying code from toggling a feature - a static site will need to be re-generated and deployed - I thought that there was value in being able to easily toggle a feature without changing its configuration or removing code within the site's templates.
Feature flags in Sculpin
My Sculpin feature flag implementation was to add a feature_flags key within
sculpin_site.yml, with each feature's name as the key and a boolean value to
set whether it's enabled - similar to how the Drupal 7 version of the
Feature Toggle module works.
This is how I added the Facebook pixel feature flag:
feature_flags:
add_facebook_pixel: true
Using the Facebook pixel feature flag
The Facebook pixel code is stored within it's own partial that I can include
from my source/_layouts/app.html.twig layout, including the pixel ID and
whether or not the feature flag is enabled.
{% include "facebook-pixel" with {
is_enabled: site.feature_flags.add_facebook_pixel,
pixel_id: site.facebook.pixel.id,
} only %}
Within the partial, I can check that both the feature flag is enabled and that there is a Facebook pixel ID, and only add the pixel code if both conditions return a truthy value.
Now the pixel can be removed just by setting add_facebook_pixel: false in
sculpin_site.yml, and without changing any other configuration or templates.
