Long lived difficult to merge feature branches, features that behave differently on staging to production and risky deployments are all things that we at CV-Library like to avoid :)

In order to make life easier for ourselves, we wrote Toggle.

Attending the London Perl Workshop (LPW 2014)? Be sure to see Tim Retout’s talk to learn more about using Toggle.

Toggle.pm is based on James Golick’s Ruby “rollout” library.

By allowing you to store feature flags in a database of your choice (it works particularly well with Redis, but just needs to be an object that supports get(), set() and del() on a key) it makes it very easy to expose a UI to the state of deployment and also to enable or disable features in real time without requiring a redeployment.

Enough talking, show me the toggling!

Say we have a shiny new feature to add to our job search. We’ll call it “job_search_NG” and we want to roll out for staff testing before a general deployment.

First we set up our storage and Toggle objects as global variables available to the whole application.

use Redis;
use Toggle;

my $redis = Redis->new;
my $toggle = Toggle->new( storage => $redis );

Then we define who we mean by “staff”. In this case, it’s for logged in users only, so we can check our permissions. The $user object must have an id accessor.

$toggle->define_group( staff => sub {
my $user = shift;
return $user->has_role('staff');
});

Now the feature needs to be activated and enabled.

Activate for our staff group (directly or via a management UI):

$toggle->activate_group( job_search_NG => 'staff' );

Enable the feature in the controller:

if ( $toggle->is_active( job_search_NG => $user ) ) {
# Show this user the shiny new feature
} else {
# Show existing feature
}

All seems fine, so now we want to share it with a particular user who isn’t staff:

$toggle->activate_user( job_search_NG => $user );

Horray, we have a go from the UX team. Let’s start a rollout to 25% of our users:

$toggle->activate_percentage( job_search_NG => 25 );

In the event of a problem, then this is all it takes to reduce the percentage in the rollout to 0:

$toggle->deactivate_percentage('job_search_NG');

And once we’re satisfied the rollout is a success, we remove the check from the controller and the old feature from the code base.

See the POD for more use cases.

Get Toggle on GitHub or CPAN.

Coming soon, our use of detailed statsd and graphite monitoring to to catch regressions in deployments.