Open Source Ecosystems

OpenFeature is an open specification that provides a vendor-agnostic, community-driven API for feature flagging that works with your favorite feature flag management tool or in-house solution.

🚀 Quick start

Requirements

It requires Elixir 1.14 or greater to run.

Install

The package can be installed by adding open_feature to your list of dependencies in mix.exs:

def deps do
  [{:open_feature, "~> 0.1"}]
end

Usage

provider = %OpenFeature.Provider.InMemory{
  flags: %{
    "v2_enabled" => %{
      disabled: false,
      default_variant: "on",
      variants: %{
        "on" => true,
        "off" => false,
      }
    }
  }
}
{:ok, provider} = OpenFeature.set_provider(provider)
client = OpenFeature.get_client()
v2_enabled = OpenFeature.Client.get_boolean_value(client, "v2_enabled", false)

API Reference

For details, including API documentation, see the respective Hex docs.

🌟 Features

Status	Features	Description
⚠️	Providers	Integrate with a commercial, open source, or in-house feature management tool.
✅	Targeting	Contextually-aware flag evaluation using evaluation context.
✅	Hooks	Add functionality to various stages of the flag evaluation life-cycle.
✅	Logging	Integrate with popular logging packages.
✅	Domains	Logically bind clients with providers.
✅	Eventing	React to state changes in the provider or flag management system.
✅	Shutdown	Gracefully clean up a provider during application shutdown.
✅	Extending	Extend OpenFeature with custom providers.

Implemented: ✅ | In-progress: ⚠️ | Not implemented yet: ❌

Providers

Providers are an abstraction between a flag management system and the OpenFeature SDK. Look here for a complete list of available providers. If the provider you're looking for hasn't been created yet, see the develop a provider section to learn how to build it yourself.

Once you've added a provider as a dependency, it can be registered with OpenFeature like this:

provider = %OpenFeature.Provider.InMemory{
  flags: %{
    "v2_enabled" => %{
      disabled: false,
      default_variant: "one",
      variants: %{
        "on" => true,
        "off" => false
      }
    }
  }
}
{:ok, provider} = OpenFeature.set_provider(provider)

In some situations, it may be beneficial to register multiple providers in the same application. This is possible using domains, which is covered in more detail below.

Targeting

Sometimes, the value of a flag must consider some dynamic criteria about the application or user, such as the user's location, IP, email address, or the server's location. In OpenFeature, we refer to this as targeting. If the flag management system you're using supports targeting, you can provide the input data using the evaluation context.

# set a value to the global context
OpenFeature.set_global_context(%{region: "us-east-1"})

# set a value to the client context
client = OpenFeature.get_client() |> OpenFeature.Client.set_context(%{region: "us-east-1"})

# set a value to the invocation context
flag_value = OpenFeature.Client.get_boolean_value(client, "some-flag", flag, %{region: "us-east-1"})

Hooks

Hooks allow for custom logic to be added at well-defined points of the flag evaluation life-cycle. Look here for a complete list of available hooks.

Once you've added a hook as a dependency, it can be registered at the client or flag invocation level.

## add a hook on this client, to run on all evaluations made by this client
client = OpenFeature.Client.add_hooks(client, [%OpenFeature.Hook{}])

## add a hook for this evaluation only
flag_value = OpenFeature.Client.get_boolean_value(client, flag_key, false, hooks: [%OpenFeature.Hook{}]);

Logging

The Elixir SDK uses the default Elixir Logger.

Domains

Clients can be assigned to a domain. A domain is a logical identifier which can be used to associate clients with a particular provider. If a domain has no associated provider, the default provider is used.

provider = %OpenFeature.Provider.InMemory{
  flags: %{
    "v2_enabled" => %{
      disabled: false,
      default_variant: "default",
      variants: %{
        "default" => true
      }
    }
  }
}

# registering the default provider
{:ok, _provider} = OpenFeature.set_provider(provider)
# registering a provider to a domain
{:ok, _provider} = OpenFeature.set_provider("my-domain", provider)

# A client bound to the default provider
default_client = OpenFeature.get_client()
# A client bound to the CachedProvider provider
domain_client = OpenFeature.get_client("my-domain")

Eventing

Events allow you to react to state changes in the provider or underlying flag management system, such as flag definition changes, provider readiness, or error conditions. Initialization events (PROVIDER_READY on success, PROVIDER_ERROR on failure) are dispatched for every provider. Some providers support additional events, such as PROVIDER_CONFIGURATION_CHANGED.

Please refer to the documentation of the provider you're using to see what events are supported.

# add an event handler to a client
OpenFeature.Client.add_event_handler(client, :provider_configuration_changed, fn event_details ->
  # do something when the provider's flag settings change
end)

Shutdown

The OpenFeature API provides a close function to perform a cleanup of all registered providers. This should only be called when your application is in the process of shutting down.

OpenFeature.shutdown()

Extending

Develop a provider

To develop a provider, you need to create a new project and include the OpenFeature SDK as a dependency. This can be a new repository or included in the existing contrib repository available under the OpenFeature organization. You’ll then need to write the provider by implementing the OpenFeature.Provider behaviour exported by the OpenFeature SDK.

defmodule OpenFeature.Provider.NoOp do
  alias OpenFeature.ResolutionDetails

  @behaviour OpenFeature.Provider

  defstruct name: "NoOp", domain: nil, state: :not_ready, hooks: []

  def initialize(provider, domain, _evaluation_context), do: {:ok, %{provider | state: :ready, domain: domain}}
  def shutdown(_provider), do: :ok

  def resolve_boolean_value(_provider, _key, default, _context), do: {:ok, %ResolutionDetails{value: default}}
  def resolve_string_value(_provider, _key, default, _context), do: {:ok, %ResolutionDetails{value: default}}
  def resolve_number_value(_provider, _key, default, _context), do: {:ok, %ResolutionDetails{value: default}}
  def resolve_map_value(_provider, _key, default, _context), do: {:ok, %ResolutionDetails{value: default}}
end