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Unleash::Client

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Unleash client so you can roll out your features with confidence.

Leverage the Unleash Server for powerful feature toggling in your ruby/rails applications.

Supported Ruby Interpreters

  • MRI 3.3
  • MRI 3.2
  • MRI 3.1
  • MRI 3.0
  • MRI 2.7
  • MRI 2.6
  • jruby 9.4
  • jruby 9.3

Installation

Add this line to your application's Gemfile:

gem 'unleash', '~> 5.0.0'

And then execute:

$ bundle

Or install it yourself as:

$ gem install unleash

Configure

It is required to configure:

  • url of the unleash server
  • app_name with the name of the runninng application.
  • custom_http_headers with {'Authorization': '<API token>'} when using Unleash v4.0.0 and later.

Please substitute the example 'https://unleash.herokuapp.com/api' for the url of your own instance.

It is highly recommended to configure:

  • instance_id parameter with a unique identifier for the running instance.
Unleash.configure do |config|
  config.app_name            = 'my_ruby_app'
  config.url                 = 'https://unleash.herokuapp.com/api'
  config.custom_http_headers = {'Authorization': '<API token>'}
end

or instantiate the client with the valid configuration:

UNLEASH = Unleash::Client.new(url: 'https://unleash.herokuapp.com/api', app_name: 'my_ruby_app', custom_http_headers: {'Authorization': '<API token>'})

Dynamic custom HTTP headers

If you need custom HTTP headers that change during the lifetime of the client, the custom_http_headers can be given as a Proc.

Unleash.configure do |config|
  config.app_name            = 'my_ruby_app'
  config.url                 = 'https://unleash.herokuapp.com/api'
  config.custom_http_headers =  proc do
    {
      'Authorization': '<API token>',
      'X-Client-Request-Time': Time.now.iso8601
    }
  end
end

List of Arguments

Argument Description Required? Type Default Value
url Unleash server URL. Y String N/A
app_name Name of your program. Y String N/A
instance_id Identifier for the running instance of program. Important so you can trace back to where metrics are being collected from. Highly recommended be be set. N String random UUID
environment Unleash context option. Could be for example prod or dev. Not yet in use. Not the same as the SDK's Unleash environment. N String default
project_name Name of the project to retrieve features from. If not set, all feature flags will be retrieved. N String nil
refresh_interval How often the unleash client should check with the server for configuration changes. N Integer 15
metrics_interval How often the unleash client should send metrics to server. N Integer 60
disable_client Disables all communication with the Unleash server, effectively taking it offline. If set, is_enabled? will always answer with the default_value and configuration validation is skipped. Will also forcefully set disable_metrics to true. Defeats the entire purpose of using unleash, except when running tests. N Boolean false
disable_metrics Disables sending metrics to Unleash server. If the disable_client option is set to true, then this option will also be set to true, regardless of the value provided. N Boolean false
custom_http_headers Custom headers to send to Unleash. As of Unleash v4.0.0, the Authorization header is required. For example: {'Authorization': '<API token>'} N Hash/Proc {}
timeout How long to wait for the connection to be established or wait in reading state (open_timeout/read_timeout) N Integer 30
retry_limit How many consecutive failures in connecting to the Unleash server are allowed before giving up. The default is to retry indefinitely. N Float::INFINITY 5
backup_file Filename to store the last known state from the Unleash server. Best to not change this from the default. N String Dir.tmpdir + "/unleash-#{app_name}-repo.json
logger Specify a custom Logger class to handle logs for the Unleash client. N Class Logger.new(STDOUT)
log_level Change the log level for the Logger class. Constant from Logger::Severity. N Constant Logger::WARN
bootstrap_config Bootstrap config on how to loaded data on start-up. This is useful for loading large states on startup without (or before) hitting the network. N Unleash::Bootstrap::Configuration nil
strategies Strategies manager that holds all strategies and allows to add custom strategies N Unleash::Strategies Unleash::Strategies.new

For a more in-depth look, please see lib/unleash/configuration.rb.

Environment Variable Description
UNLEASH_BOOTSTRAP_FILE File to read bootstrap data from
UNLEASH_BOOTSTRAP_URL URL to read bootstrap data from

Usage in a plain Ruby Application

require 'unleash'
require 'unleash/context'

@unleash = Unleash::Client.new(app_name: 'my_ruby_app', url: 'https://unleash.herokuapp.com/api', custom_http_headers: { 'Authorization': '<API token>' })

feature_name = "AwesomeFeature"
unleash_context = Unleash::Context.new
unleash_context.user_id = 123

if @unleash.is_enabled?(feature_name, unleash_context)
  puts " #{feature_name} is enabled according to unleash"
else
  puts " #{feature_name} is disabled according to unleash"
end

if @unleash.is_disabled?(feature_name, unleash_context)
  puts " #{feature_name} is disabled according to unleash"
else
  puts " #{feature_name} is enabled according to unleash"
end

Usage in a Rails Application

Add Initializer

Put in config/initializers/unleash.rb:

Unleash.configure do |config|
  config.app_name = Rails.application.class.parent.to_s
  config.url      = 'https://unleash.herokuapp.com/api'
  # config.instance_id = "#{Socket.gethostname}"
  config.logger   = Rails.logger
end

UNLEASH = Unleash::Client.new

# Or if preferred:
# Rails.configuration.unleash = Unleash::Client.new

For config.instance_id use a string with a unique identification for the running instance. For example: it could be the hostname, if you only run one App per host. Or the docker container id, if you are running in docker. If it is not set the client will generate an unique UUID for each execution.

To have it available in the rails console command as well, also add to the file above:

Rails.application.console do
  UNLEASH = Unleash::Client.new
  # or
  # Rails.configuration.unleash = Unleash::Client.new
end

Add Initializer if using Puma in clustered mode

That is, multiple workers configured in puma.rb:

workers ENV.fetch("WEB_CONCURRENCY") { 2 }
with preload_app!

Then you may keep the client configuration still in config/initializers/unleash.rb:

Unleash.configure do |config|
  config.app_name    = Rails.application.class.parent.to_s
  config.url                 = 'https://unleash.herokuapp.com/api'
  config.custom_http_headers = {'Authorization': '<API token>'}
end

But you must ensure that the unleash client is instantiated only after the process is forked. This is done by creating the client inside the on_worker_boot code block in puma.rb as below:

#...
preload_app!
#...

on_worker_boot do
  # ...

  ::UNLEASH = Unleash::Client.new
end

on_worker_shutdown do
  ::UNLEASH.shutdown
end
without preload_app!

By not using preload_app!:

  • the Rails constant will NOT be available.
  • but phased restarts will be possible.

You need to ensure that in puma.rb:

  • loading unleash sdk with require 'unleash' explicitly, as it will not be pre-loaded.
  • all parameters must be explicitly set in the on_worker_boot block, as config/initializers/unleash.rb is not read.
  • there are no references to Rails constant, as that is not yet available.

Example for puma.rb:

require 'unleash'

#...
# no preload_app!

on_worker_boot do
  # ...

  ::UNLEASH = Unleash::Client.new(
    app_name: 'my_rails_app',
    url: 'https://unleash.herokuapp.com/api',
    custom_http_headers: {'Authorization': '<API token>'},
  )
end

on_worker_shutdown do
  ::UNLEASH.shutdown
end

Note that we also added shutdown hooks in on_worker_shutdown, to ensure a clean shutdown.

Add Initializer if using Phusion Passenger

The unleash client needs to be configured and instantiated inside the PhusionPassenger.on_event(:starting_worker_process) code block due to smart spawning:

The initializer in config/initializers/unleash.rb should look like:

PhusionPassenger.on_event(:starting_worker_process) do |forked|
  if forked
    Unleash.configure do |config|
      config.app_name    = Rails.application.class.parent.to_s
      # config.instance_id = "#{Socket.gethostname}"
      config.logger      = Rails.logger
      config.url                 = 'https://unleash.herokuapp.com/api'
      config.custom_http_headers = {'Authorization': '<API token>'}
    end

    UNLEASH = Unleash::Client.new
  end
end

Add Initializer hooks when using within Sidekiq

Note that in this case we require that the code block for Unleash.configure is set beforehand. For example in config/initializers/unleash.rb.

Sidekiq.configure_server do |config|
  config.on(:startup) do
    UNLEASH = Unleash::Client.new
  end

  config.on(:shutdown) do
    UNLEASH.shutdown
  end
end

Set Unleash::Context

Be sure to add the following method and callback in the application controller to have @unleash_context set for all requests:

Add in app/controllers/application_controller.rb:

  before_action :set_unleash_context

  private
  def set_unleash_context
    @unleash_context = Unleash::Context.new(
      session_id: session.id,
      remote_address: request.remote_ip,
      user_id: session[:user_id]
    )
  end

Or if you see better fit, only in the controllers that you will be using unleash.

Sample usage

Then wherever in your application that you need a feature toggle, you can use:

if UNLEASH.is_enabled? "AwesomeFeature", @unleash_context
  puts "AwesomeFeature is enabled"
end

or if client is set in Rails.configuration.unleash:

if Rails.configuration.unleash.is_enabled? "AwesomeFeature", @unleash_context
  puts "AwesomeFeature is enabled"
end

If you don't want to check a feature is disabled with unless, you can also use is_disabled?:

# so instead of:
unless UNLEASH.is_enabled? "AwesomeFeature", @unleash_context
  puts "AwesomeFeature is disabled"
end

# it might be more intelligible:
if UNLEASH.is_disabled? "AwesomeFeature", @unleash_context
  puts "AwesomeFeature is disabled"
end

If the feature is not found in the server, it will by default return false. However, you can override that by setting the default return value to true:

if UNLEASH.is_enabled? "AwesomeFeature", @unleash_context, true
  puts "AwesomeFeature is enabled by default"
end
# or
if UNLEASH.is_disabled? "AwesomeFeature", @unleash_context, true
  puts "AwesomeFeature is disabled by default"
end

Another possibility is to send a block, Lambda or Proc to evaluate the default value:

net_check_proc = proc do |feature_name, context|
  context.remote_address.starts_with?("10.0.0.")
end

if UNLEASH.is_enabled?("AwesomeFeature", @unleash_context, &net_check_proc)
  puts "AwesomeFeature is enabled by default if you are in the 10.0.0.* network."
end

or

awesomeness = 10
@unleash_context.properties[:coolness] = 10

if UNLEASH.is_enabled?("AwesomeFeature", @unleash_context) { |feat, ctx| awesomeness >= 6 && ctx.properties[:coolness] >= 8 }
  puts "AwesomeFeature is enabled by default if both the user has a high enough coolness and the application has a high enough awesomeness"
end

Note:

  • The block/lambda/proc can use feature name and context as an arguments.
  • The client will evaluate the fallback function once per call of is_enabled(). Please keep this in mind when creating your fallback function!
  • The returned value of the block should be a boolean. However, the client will coerce the result to boolean via !!.
  • If both a default_value and fallback_function are supplied, the client will define the default value by ORing the default value and the output of the fallback function.

Alternatively by using if_enabled (or if_disabled) you can send a code block to be executed as a parameter:

UNLEASH.if_enabled "AwesomeFeature", @unleash_context, true do
  puts "AwesomeFeature is enabled by default"
end

Note: if_enabled (and if_disabled) only support default_value, but not fallback_function.

Variations

If no variant is found in the server, use the fallback variant.

fallback_variant = Unleash::Variant.new(name: 'default', enabled: true, payload: {"color" => "blue"})
variant = UNLEASH.get_variant "ColorVariants", @unleash_context, fallback_variant

puts "variant color is: #{variant.payload.fetch('color')}"

Bootstrapping

Bootstrap configuration allows the client to be initialized with a predefined set of toggle states. Bootstrapping can be configured by providing a bootstrap configuration when initializing the client.

@unleash = Unleash::Client.new(
    url: 'https://unleash.herokuapp.com/api',
    app_name: 'my_ruby_app',
    custom_http_headers: { 'Authorization': '<API token>' },
    bootstrap_config: Unleash::Bootstrap::Configuration.new({
        url: "https://unleash.herokuapp.com/api/client/features",
        url_headers: {'Authorization': '<API token>'}
    })
)

The Bootstrap::Configuration initializer takes a hash with one of the following options specified:

  • file_path - An absolute or relative path to a file containing a JSON string of the response body from the Unleash server. This can also be set though the UNLEASH_BOOTSTRAP_FILE environment variable.
  • url - A url pointing to an Unleash server's features endpoint, the code sample above is illustrative. This can also be set though the UNLEASH_BOOTSTRAP_URL environment variable.
  • url_headers - Headers for the GET http request to the url above. Only used if the url parameter is also set. If this option isn't set then the bootstrapper will use the same url headers as the Unleash client.
  • data - A raw JSON string as returned by the Unleash server.
  • block - A lambda containing custom logic if you need it, an example is provided below.

You should only specify one type of bootstrapping since only one will be invoked and the others will be ignored. The order of preference is as follows:

  • Select a data bootstrapper if it exists.
  • If no data bootstrapper exists, select the block bootstrapper.
  • If no block bootstrapper exists, select the file bootstrapper from either parameters or the specified environment variable.
  • If no file bootstrapper exists, then check for a URL bootstrapper from either the parameters or the specified environment variable.

Example usage:

First saving the toggles locally:

curl -H 'Authorization: <API token>' -XGET 'https://unleash.herokuapp.com/api' > ./default-toggles.json

Now using them on start up:

custom_boostrapper = lambda {
  File.read('./default-toggles.json')
}

@unleash = Unleash::Client.new(
    app_name: 'my_ruby_app',
    url: 'https://unleash.herokuapp.com/api',
    custom_http_headers: { 'Authorization': '<API token>' },
    bootstrap_config: Unleash::Bootstrap::Configuration.new({
        block: custom_boostrapper
    })
)

This example could be easily achieved with a file bootstrapper, this is just to illustrate the usage of custom bootstrapping. Be aware that the client initializer will block until bootstrapping is complete.

Client methods

Method Name Description Return Type
is_enabled? Check if feature toggle is to be enabled or not. Boolean
enabled? Alias to the is_enabled? method. But more ruby idiomatic. Boolean
if_enabled Run a code block, if a feature is enabled. yield
is_disabled? Check if feature toggle is to be enabled or not. Boolean
disabled? Alias to the is_disabled? method. But more ruby idiomatic. Boolean
if_disabled Run a code block, if a feature is disabled. yield
get_variant Get variant for a given feature Unleash::Variant
shutdown Save metrics to disk, flush metrics to server, and then kill ToggleFetcher and MetricsReporter threads. A safe shutdown. Not really useful in long running applications, like web applications. nil
shutdown! Kill ToggleFetcher and MetricsReporter threads immediately. nil

For the full method signatures, please see client.rb

Local test client

# cli unleash client:
bundle exec bin/unleash-client --help

# or a simple sample implementation (with values hardcoded):
bundle exec examples/simple.rb

Available Strategies

This client comes with the all the required strategies out of the box:

  • ApplicationHostnameStrategy
  • DefaultStrategy
  • FlexibleRolloutStrategy
  • GradualRolloutRandomStrategy
  • GradualRolloutSessionIdStrategy
  • GradualRolloutUserIdStrategy
  • RemoteAddressStrategy
  • UnknownStrategy
  • UserWithIdStrategy

Custom Strategies

Client allows to add custom activation strategies using configuration. In order for strategy to work correctly it should support two methods name and is_enabled?

class MyCustomStrategy
  def name
    'myCustomStrategy'
  end

  def is_enabled?(params = {}, context = nil)
    true
  end
end

Unleash.configure do |config|
  config.strategies.add(MyCustomStrategy.new)
end

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

This SDK is also built against the Unleash Client Specification tests. To run the Ruby SDK against this test suite, you'll need to have a copy on your machine, you can clone the repository directly using:

git clone --depth 5 --branch v5.0.2 https://github.com/Unleash/client-specification.git client-specification

After doing this, rake spec will also run the client specification tests.

To install this gem onto your local machine, run bundle exec rake install.

Releasing

Choose a new version number following Semantic Versioning semantics and then:

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/unleash/unleash-client-ruby.

Be sure to run both bundle exec rspec and bundle exec rubocop in your branch before creating a pull request.

Please include tests with any pull requests, to avoid regressions.

Check out our guide for more information on how to build and scale feature flag systems