Quickstart

The Eppo Elixir SDK enables feature flags and experiments in your Elixir applications with only a few lines of code.

The SDK handles all the complexity of feature flag evaluation and experiment assignment locally in your application, with no network calls required after initial setup. This guide will walk you through installing the SDK and implementing your first feature flag and experiment.

Installation

First, add the SDK as a dependency in your mix.exs:

defp deps do
  [
    {:eppo_sdk, "~> 1.0"}
  ]
end

Then fetch and compile dependencies:

mix deps.get

Feature Flags

Feature flags are a way to toggle features on and off without needing to deploy code.

Initialize the SDK

Create an SDK key if you don't already have one.

First, initialize the SDK using your SDK key:

config = %EppoSdk.Client.Config{
  api_key: "<SDK-KEY>",
  assignment_logger: MyApp.AssignmentLogger
}

{:ok, client} = EppoSdk.Client.new(config)

note

The SDK key is different from the project API key. You can find your SDK key in the SDK Keys section of the Eppo interface.

Assign a variant

Once initialized, you can start making assignments:

user = get_current_user()

variation = EppoSdk.Client.get_string_assignment(
  client,
  "show-new-feature",
  user.id,
  %{ "country" => user.country },
  "default"
)

case variation do
  "variant-a" -> handle_variant_a()
  "variant-b" -> handle_variant_b()
  _ -> handle_control()
end

Assignment Types

The SDK provides different assignment functions based on the type of value you need:

Function	Return Type
get_string_assignment/5	String
get_boolean_assignment/5	Boolean
get_json_assignment/5	Map (JSON object)
get_integer_assignment/5	Integer
get_numeric_assignment/5	Float

note

See more details about assignment functions in the Assignments page.

Assignment Logger

While feature flags are useful, they do not send you any information about how your users are interacting with the feature. To run and analyze experiments, we need to collect data about these interactions using your preferred logging system. Implement the EppoSdk.AssignmentLogger behavior to log events through the SDK:

defmodule MyApp.AssignmentLogger do
  @behaviour EppoSdk.AssignmentLogger
  
  def log_assignment(assignment) do
    IO.inspect("Logging assignment: #{inspect(assignment)}") # Replace with actual logging logic
  end
end

config = %EppoSdk.Client.Config{
  api_key: "<SDK-KEY>",
  assignment_logger: MyApp.AssignmentLogger
}

{:ok, client} = EppoSdk.Client.new(config)

note

In a production application, you would want to replace IO.inspect with an actual logging system. We have documentation on how to set up logging with multiple popular data warehouses and logging systems in the Assignments page.

Singleton Server

We want to avoid re-initializing the SDK for each request. Instead of passing the client around, we can use the EppoSdk.Server module to get the current client

config = %EppoSdk.Client.Config{
  api_key: api_key,
  assignment_logger: EppoSdk.AssignmentLogger,
  is_graceful_mode: true,
  poll_interval_seconds: 30,
  poll_jitter_seconds: 3
}

{:ok, _pid} = EppoSdk.Server.start_link(config)
client = EppoSdk.Server.get_instance()

You can also add this server to your supervision tree:

Or added to your application's supervision tree:

# In your application.ex
defmodule YourApp.Application do
  use Application

  def start(_type, _args) do
    config = %EppoSdk.Client.Config{
      api_key: System.get_env("EPPO_API_KEY"),
      assignment_logger: YourApp.AssignmentLogger,
      # ... other config options ...
    }

    children = [
      # ... other children ...
      {EppoSdk.Server, config}
    ]

    opts = [strategy: :one_for_one, name: YourApp.Supervisor]
    Supervisor.start_link(children, opts)
  end
end