rollout

Feature flippers.

MAKE SURE TO READ THIS: 2.X Changes and Migration Path

As of rollout-2.x, only one key is used per feature for performance reasons. The serialized format is percentage|user_id,user_id,...|group,_group...|data_json. This has the effect of making concurrent feature modifications unsafe, but in practice, I doubt this will actually be a problem.

This also has the effect of rollout no longer being dependent on redis. Just give it something that responds to set(key,value), get(key) and del(key).

Install it

gem install rollout

How it works

Initialize a rollout object. I assign it to a global var.

require 'redis'

$redis   = Redis.new
$rollout = Rollout.new($redis)

Update data specific to a feature:

@rollout.set_feature_data(:chat, description: 'foo', release_date: 'bar', whatever: 'baz')

Check whether a feature is active for a particular user:

$rollout.active?(:chat, User.first) # => true/false

Check whether a feature is active globally:

$rollout.active?(:chat)

You can activate features using a number of different mechanisms.

Groups

Rollout ships with one group by default: "all", which does exactly what it sounds like.

You can activate the all group for the chat feature like this:

$rollout.activate_group(:chat, :all)

You might also want to define your own groups. We have one for our caretakers:

$rollout.define_group(:caretakers) do |user|
  user.caretaker?
end

You can activate multiple groups per feature.

Deactivate groups like this:

$rollout.deactivate_group(:chat, :all)

Specific Users

You might want to let a specific user into a beta test or something. If that user isn't part of an existing group, you can let them in specifically:

$rollout.activate_user(:chat, @user)

Deactivate them like this:

$rollout.deactivate_user(:chat, @user)

User Percentages

If you're rolling out a new feature, you might want to test the waters by slowly enabling it for a percentage of your users.

$rollout.activate_percentage(:chat, 20)

The algorithm for determining which users get let in is this:

CRC32(user.id) % 100_000 < percentage * 1_000

So, for 20%, users 0, 1, 10, 11, 20, 21, etc would be allowed in. Those users would remain in as the percentage increases.

Deactivate all percentages like this:

$rollout.deactivate_percentage(:chat)

Note that activating a feature for 100% of users will also make it active "globally". That is when calling Rollout#active? without a user object.

In some cases you might want to have a feature activated for a random set of users. It can come specially handy when using Rollout for split tests.

$rollout = Rollout.new($redis, randomize_percentage: true)

When on randomize_percentage will make sure that 50% of users for feature A are selected independently from users for feature B.

Global actions

While groups can come in handy, the actual global setter for a feature does not require a group to be passed.

$rollout.activate(:chat)

In that case you can check the global availability of a feature using the following

$rollout.active?(:chat)

And if something is wrong you can set a feature off for everybody using

Deactivate everybody at once:

$rollout.deactivate(:chat)

For many of our features, we keep track of error rates using redis, and deactivate them automatically when a threshold is reached to prevent service failures from cascading. See https://github.com/jamesgolick/degrade for the failure detection code.

Namespacing

Rollout separates its keys from other keys in the data store using the "feature" keyspace.

If you're using redis, you can namespace keys further to support multiple environments by using the redis-namespace gem.

$ns = Redis::Namespace.new(Rails.env, redis: $redis)
$rollout = Rollout.new($ns)
$rollout.activate_group(:chat, :all)

This example would use the "development:feature:chat:groups" key.

Implementations in other languages

Python: https://github.com/asenchi/proclaim
PHP: https://github.com/opensoft/rollout
Clojure: https://github.com/yeller/shoutout

Contributors

James Golick - Creator - https://github.com/jamesgolick
Eric Rafaloff - Maintainer - https://github.com/EricR