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    Rust SDK reference

    Read time: 1 minute
    Last edited: Sep 27, 2022
    This SDK is in beta

    Development work on the Rust SDK is ongoing. Elements of this SDK may change without notice. Do not use this SDK in production environments.


    This topic documents how to get started with the server-side Rust SDK, and links to reference information on all of the supported features.

    SDK quick links

    LaunchDarkly's SDKs are open source. In addition to this reference guide, we provide source, API reference documentation, and a sample application:

    SDK API documentationSDK API docs
    GitHub repositoryrust-server-sdk
    Sample applicationhello-rust
    Published modulecrates.io

    Getting started

    After you complete the Getting Started process, follow these instructions to start using the LaunchDarkly SDK in your Rust application.

    First, install the LaunchDarkly SDK as a dependency in your application.

    cargo install cargo-edit
    cargo add launchdarkly-server-sdk --allow-prerelease

    Next, import the LaunchDarkly client in your application code:

    use launchdarkly_server_sdk::{Client, ConfigBuilder, User};

    After you install and import the SDK, create a single, shared instance of the LaunchDarkly client. Specify your SDK key here so that your application is authorized to connect to LaunchDarkly, your application, and your environment.

    Once you have created the client, start the client process and wait for the client to initialize. This SDK depends on the tokio crate to provide a default runtime and as such it is a required dependency.

    Only create one instance of client.

    Here's how:

    async fn main () {
    let config = ConfigBuilder::new(&sdk_key).build();
    let client = Client::build(config).unwrap();
    if !client.initialized_async().await {
    panic!("Client failed to successfully initialize");
    client must be a singleton

    It's important to make client a singleton. The client instance maintains internal state that allows LaunchDarkly to serve feature flags without making any remote requests. Do not instantiate a new client with every request.

    You can use client to check which variation a particular user will receive for a given feature flag.

    Here's how:

    let user = User::with_key("user@test.com").build();
    let show_feature = client.bool_variation(&user, "your.flag.key", false);
    if show_feature {
    # application code to show the feature
    } else {
    # the code to run if the feature is off

    Supported features

    This SDK supports the following features: