> For clean Markdown of any page, append .md to the page URL. > For a complete documentation index, see https://docs.getunleash.io/sdks/ruby/llms.txt. > For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.getunleash.io/_mcp/server. # Ruby > Set up the Unleash Ruby SDK to evaluate feature flags with context, variants, bootstrap, custom strategies, and Rails support. The Unleash Ruby SDK lets you evaluate feature flags in Ruby applications. It connects to Unleash or [Unleash Edge](/unleash-edge) to fetch flag configurations and evaluates them locally against an [Unleash context](/concepts/unleash-context). You can use this SDK with [Unleash Enterprise](https://www.getunleash.io/pricing) or [Unleash Open Source](https://github.com/Unleash/unleash). For an overview of how Unleash SDKs work, including offline behavior, feature compatibility across SDKs, and default refresh and metrics intervals, refer to the [SDK overview](/sdks). ## Requirements * Ruby (MRI) 2.7 or later * JRuby 9.4 or later ## Installation Add this line to your application's Gemfile: ```ruby gem 'unleash', '~> 6.4.1' ``` And then execute: ```bash bundle ``` Or install it yourself as: ```bash gem install unleash ``` ## Configuration It is **required** to configure: * `app_name` with the name of the running application * `url` of your Unleash server * `custom_http_headers` with `{'Authorization': ''}` when using Unleash v4+ It is **highly recommended** to configure: * `instance_id` parameter with a unique identifier for the running instance ```ruby Unleash.configure do |config| config.app_name = 'my_ruby_app' config.url = '/api' config.custom_http_headers = {'Authorization': ''} end ``` or instantiate the client with the valid configuration: ```ruby UNLEASH = Unleash::Client.new(url: '/api', app_name: 'my_ruby_app', custom_http_headers: {'Authorization': ''}) ``` ## Dynamic custom HTTP headers If you need custom HTTP headers that change during the lifetime of the client, you can pass `custom_http_headers` as a `Proc`. ```ruby Unleash.configure do |config| config.app_name = 'my_ruby_app' config.url = '/api' config.custom_http_headers = proc do { 'Authorization': '', 'X-Client-Request-Time': Time.now.iso8601 } end end ``` ### Configuration options | 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 your program—set this to be able trace where metrics are being collected from. | N | String | random UUID | | `environment` | Unleash context option, for example, `prod` or `dev`. Not yet in use. **Not** the same as the SDK's [Unleash environment](/concepts/environments). | N | String | `default` | | `project_name` | Name of the project to retrieve feature flags 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?` 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': ''}`. | 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. It is 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 for loading data on startup—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 ```ruby require 'unleash' require 'unleash/context' @unleash = Unleash::Client.new(app_name: 'my_ruby_app', url: '/api', custom_http_headers: { 'Authorization': '' }) 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 The initializer setup varies depending on whether you're using a standard setup, Puma in clustered mode, Phusion Passenger, or Sidekiq. #### Standard Rails applications Put in `config/initializers/unleash.rb`: ```ruby Unleash.configure do |config| config.app_name = Rails.application.class.module_parent_name config.url = '' # config.instance_id = "#{Socket.gethostname}" config.logger = Rails.logger config.custom_http_headers = {'Authorization': ''} 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 not set, the client will generate a unique UUID for each execution. To have it available in the `rails console` command as well, also add to the file above: ```ruby Rails.application.console do UNLEASH = Unleash::Client.new # or # Rails.configuration.unleash = Unleash::Client.new end ``` #### Puma in clustered mode When using [Puma](https://github.com/puma/puma) with multiple workers configured in `puma.rb`: ```ruby workers ENV.fetch("WEB_CONCURRENCY") { 2 } ``` ##### With `preload_app!` Then you may keep the client configuration still in `config/initializers/unleash.rb`: ```ruby Unleash.configure do |config| config.app_name = Rails.application.class.parent.to_s config.url = '/api' config.custom_http_headers = {'Authorization': ''} 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: ```ruby #... 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. * Phased restarts will be possible. You need to ensure that in `puma.rb`: * The Unleash SDK is loaded with `require 'unleash'` explicitly, as it will not be pre-loaded. * All parameters are set explicitly 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`: ```ruby require 'unleash' #... # no preload_app! on_worker_boot do # ... ::UNLEASH = Unleash::Client.new( app_name: 'my_rails_app', url: '/api', custom_http_headers: {'Authorization': ''}, ) end on_worker_shutdown do ::UNLEASH.shutdown end ``` Note that we also added shutdown hooks in `on_worker_shutdown`, to ensure a clean shutdown. #### Phusion Passenger When using [Phusion Passenger](https://github.com/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](https://www.phusionpassenger.com/library/indepth/ruby/spawn_methods/#smart-spawning-caveats): The initializer in `config/initializers/unleash.rb` should look like: ```ruby 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 = '/api' config.custom_http_headers = {'Authorization': ''} end UNLEASH = Unleash::Client.new end end ``` #### Sidekiq When using [Sidekiq](https://github.com/sidekiq/sidekiq), the code block for `Unleash.configure` must be set beforehand. For example in `config/initializers/unleash.rb`. ```ruby Sidekiq.configure_server do |config| config.on(:startup) do UNLEASH = Unleash::Client.new end config.on(:shutdown) do UNLEASH.shutdown end end ``` ### Unleash context 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`: ```ruby 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 ``` Alternatively, you can add this method only to the controllers that use Unleash. ### Example usage Then wherever in your application that you need a feature toggle, you can use: ```ruby if UNLEASH.is_enabled? "AwesomeFeature", @unleash_context puts "AwesomeFeature is enabled" end ``` or if client is set in `Rails.configuration.unleash`: ```ruby 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?`: ```ruby # 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`: ```ruby 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](https://ruby-doc.org/core-3.0.1/Kernel.html#method-i-lambda) or [Proc](https://ruby-doc.org/core-3.0.1/Proc.html#method-i-yield) to evaluate the default value: ```ruby 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 ```ruby 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 the feature name and context as 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 a boolean via `!!`. * If both a `default_value` and `fallback_function` are supplied, the client will define the default value by `OR`ing 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: ```ruby 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`. ### Check variants If no flag is found in the server, use the fallback variant. ```ruby 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')}" ``` ## Bootstrap 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. ```ruby @unleash = Unleash::Client.new( url: '/api', app_name: 'my_ruby_app', custom_http_headers: { 'Authorization': '' }, bootstrap_config: Unleash::Bootstrap::Configuration.new({ url: "/api/client/features", url_headers: {'Authorization': ''} }) ) ``` 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 through 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 through 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, save the toggles locally: ```shell curl -H 'Authorization: ' -XGET '/api' > ./default-toggles.json ``` Then use them on startup: ```ruby custom_boostrapper = lambda { File.read('./default-toggles.json') } @unleash = Unleash::Client.new( app_name: 'my_ruby_app', url: '/api', custom_http_headers: { 'Authorization': '' }, 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?` | Checks if a feature toggle is enabled or not | Boolean | | `enabled?` | A more idiomatic Ruby alias for the `is_enabled?` method | Boolean | | `if_enabled` | Runs a code block, if a feature is enabled | `yield` | | `is_disabled?` | Checks if feature toggle is enabled or not | Boolean | | `disabled?` | A more idiomatic Ruby alias for the `is_disabled?` method | Boolean | | `if_disabled` | Runs a code block, if a feature is disabled | `yield` | | `get_variant` | Gets variant for a given feature | `Unleash::Variant` | | `shutdown` | Saves metrics to disk, flushes metrics to server, and then kills `ToggleFetcher` and `MetricsReporter` threads—a safe shutdown, not generally needed in long-running applications, like web applications | nil | | `shutdown!` | Kills `ToggleFetcher` and `MetricsReporter` threads immediately | nil | For the full method signatures, see [client.rb](https://github.com/Unleash/unleash-ruby-sdk/blob/main/lib/unleash/client.rb). ## Built-in activation strategies This client comes with all the required strategies out of the box: * ApplicationHostnameStrategy * DefaultStrategy * FlexibleRolloutStrategy * GradualRolloutRandomStrategy * GradualRolloutSessionIdStrategy * GradualRolloutUserIdStrategy * RemoteAddressStrategy * UserWithIdStrategy ## Custom strategies You can add [custom activation strategies](/concepts/custom-activation-strategies) using configuration. In order for the strategy to work correctly it should support two methods `name` and `is_enabled?`. ```ruby 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 ``` Check out our guide for more information on how to build and scale [feature flag systems](/guides/feature-flag-best-practices). ## Migrating to v6 If you use [custom strategies](#custom-strategies) or override built-in ones, read the complete [v6 migration guide](https://github.com/Unleash/unleash-ruby-sdk/blob/main/./v6_MIGRATION_GUIDE.md) before upgrading. > Set up the Unleash Ruby SDK to evaluate feature flags with context, variants, bootstrap, custom strategies, and Rails support.