Erlang SDK reference

Overview

This reference guide documents all of the methods available in the Erlang SDK, and explains how these methods work. LaunchDarkly's SDKs are open source. The source is available in its GitHub repository and its generated API reference.

You can also use this SDK to clone and run a sample application with Erlang, Elixir, or the Phoenix framework.

Getting started

Follow the steps below to get started using the LaunchDarkly SDK in your Erlang application.

First, download the dependency using Rebar:

{deps, [
  {ldclient, "1.0.0", {pkg, launchdarkly_server_sdk}}
]}.
COPY

Then, add it to your app.src file:

{applications,
  [kernel,
  stdlib,
  ldclient
]},
COPY

If you use Elixir, you can download the dependency using Mix:

defp deps do
  [
    {:ldclient, "~> 1.0.0", hex: :launchdarkly_server_sdk}
  ]
end
COPY

After you install the SDK dependency, create an instance of the SDK.

Here is an example:

% This starts an instance with the default options
ldclient:start_instance("YOUR_SDK_KEY")
% You can also start a named instance
ldclient:start_instance("YOUR_SDK_KEY", my_instance)
COPY

Next, check which flag variation a specific user should receive:

Flag = ldclient:variation(<<"YOUR_FLAG_KEY">>, #{key => <<"123">>}, false)
COPY

Transport Layer Security (TLS)

The SDK includes configuration options that allow you to set custom TLS options. If you don't set these options, then the SDK will use the Erlang/OTP defaults. The default TLS connection settings in Erlang/OTP do not validate the identity or authenticity of certificates.

If your application has existing TLS options, then you can pass them to the SDK:

ldclient:start_instance(SdkKey, #{
  http_options => #{
      tls_options => YourOptions
  }}),
COPY

The SDK also provides helper methods to create TLS options. We recommend ensuring that the SDK is using a Certificate Authorities (CA) store that is regularly updated for production environments.

Here is a list of helper methods:

• ldclient_config:tls_basic_options(): This helper provides a basic TLS configuration suitable for development. It tries to use a CA store in the default location for many linux distributions (/etc/ssl/certs/ca-certificates.crt). If it can't find the store, then it will use the store from the certifi package.
• ldclient_config:tls_basic_linux_options(): This helper provides a basic TLS configuration for linux. It uses the CA store located at /etc/ssl/certs/ca-certificates.crt.
• ldclient_config:tls_ca_certfile_options(CaStorePath): This helper provides a basic TLS configuration with the CA store you specify.
• ldclient_config:tls_basic_certifi_options(): This helper provides a basic TLS configuration that uses the certifi store. Because this store is from a dependency of the package, it is not maintained or updated by OS releases.
• ldclient_config:with_tls_revocation(TlsOptions): This helper extends a TLS configuration with certificate revocation. Revocation is not included in the basic configuration because the Erlang/OTP does not cache revocation results. Enabling this feature incurs additional requests per request the SDK makes.

Shutting down

Lastly, shut down the client when your application terminates. To learn more, read Shutting down.

Supported features

This SDK supports the following features:

• Configuration
• Evaluating flags
• Flag evaluation reasons
• Getting all flags
• Identifying and changing users
• Offline mode
• Reading flags from a file
• Sending custom events
• Shutting down
• Storing data
• User configuration