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Erlang SDK reference

Read time: 2 minutes
Last edited: Jan 08, 2022

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}}
]}.

Then, add it to your app.src file:

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

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

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

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

Use a single instance

The Erlang SDK supports starting multiple instances, but most use cases only need a single instance. Consider using multiple instances only if you need to simultaneously access more than one environment. Do not start an instance every time you need to make a variation or other SDK call.

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)

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

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

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
}}),

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: