Feature Switches

Status: Alpha (Don't use in production)

Summary

A gem that manages features switches in an application. Feature switches are
dynamically configured. They can be turned on, on to a percentage of actors, on
to a specific group of actors, or off without a code deploy. There are some
excellent and mature projects that provide this functionality already:
rollout and
flipper. This project is an experiment
aiming for a specific set of design goals:

Reduce the chatter in the protocol between a node checking to see if a
feature is enabled for an actor and the backend storage system. We're going to
be reading this data far more often than we're writing it so we want to
aggressively cache, but...
Ensure all nodes get the latest configuration data as soon as possible. A
cache that expires after a certain TTL can't work as a client isn't guaranteed
to talk to the same instance of our application on each request. A feature
disappearing and reappearing depending on which application server instance a
user hits is a bug.
Allow for extension with new backends that support change notification;
specifically distributed system synchronization backends like Zookeeper.
Ensure that any kind of actor identifier can be used; not just an object that
responds to id We want to gate our switches on things that aren't ActiveRecord
objects (e.g., incoming phone numbers, username, etc).
Expose an easy-to-remember CLI since irb is how we'll configure the feature
switches.

Supported Backends

Redis
Postgres
In-memory (for testing)

Design

Switches uses a backend for both storage of feature configuration data and for
notifying sibling nodes that a change has been made. We'll look at how this
works against the Redis backend.

On startup, switches will connect to Redis twice: once for querying and setting
configuration data and one for subscribing to a pub/sub channel of change
notifications. When a change is made to configuration data, an extra call is
made to Redis to publish a change notification. Once this change notification is
received by other listening nodes they will refetch the configuration data
and update their local stores.

This allows a node to validate if a user can pass through a feature switch using
in-memory data without a querying a backend but ensures that each node is using
the same data to make the decision.

Installation

In your Gemfile:

  gem "feature_switches"

Postgres Backend

Note that switches will connect to Postgres twice for each node. This is important
as Postgres will fork a new process for each connection so ensure you have the
overhead before using this backend.

To use Postgres a table called switches must be created in your database.
Two rake tasks have been included to create and drop this table:

Add this to your Rakefile:

  require "switches"
  require "switches/tasks"

To create the table:

  DATABASE_URL=postgres://root:sekret@localhost/my_application rake switches:postgres:setup

To drop the table

  DATABASE_URL=postgres://root:sekret@localhost/my_application rake switches:postgres:remove

Usage

# Initialize
$switches = Switches do |config|
  config.backend = "redis://localhost:6379/0"
end
# => #<Switches redis://localhost:6379/0>

# Check to see if a feature is active for an identifier
$switches.feature(:redesign).on?(current_user.id)
# => true

$switches.feature(:redesign).on?(current_user.phone_number)
# => true

# Turn a feature on globally
$switches.feature(:redesign).on
# => #<Feature redesign; 100%>

# Turn a feature on for a given percentage of identifiers
$switches.feature(:redesign).on(25)
# => #<Feature redesign; 25%>

# Turn a feature off globally
$switches.feature(:redesign).off
# => #<Feature redesign; 0%>

# Add or remove an identifier from a cohort group
$switches.cohort(:power_users).add(424)
# => #<Cohort power_users; 1 member>

$switches.cohort(:power_users).remove(424)
# => #<Cohort power_users; 0 members>

# Add a cohort group to a feature
$switches.feature(:redesign).add(:power_users)
# => #<Feature redesign; 0%; power_users>

# Remove a cohort group from a feature
$switches.feature(:redesign).remove(:power_users)
# => #<Feature redesign; 0%>

License

Please see LICENSE.

jpignata/switches