/onboarding

.NET (Server) — SDK detail

• Official docs: .NET SDK reference (server-side)
• API reference: Server SDK API
• Published package: LaunchDarkly.ServerSdk (NuGet)
• Recipe (detect / install): SDK Recipes (.NET Server)

Target the current major server SDK on NuGet (LaunchDarkly.ServerSdk); follow the docs for version compatibility (.NET SDK reference).

Install: From the project directory (Install the SDK):

dotnet add package LaunchDarkly.ServerSdk

Optional observability (.NET observability) — requires server SDK 8.10+:

dotnet add package LaunchDarkly.Observability

Import: Namespace differs from the package name (same page — import):

using LaunchDarkly.Sdk;
using LaunchDarkly.Sdk.Server;

// Optional — LaunchDarkly.Observability package; requires server SDK 8.10+
// using LaunchDarkly.Observability;

Initialize: Use Configuration.Builder(sdkKey) with StartWaitTime (docs recommend a short wait so a bad network does not hang forever). Construct LdClient before builder.Build() (Initialize the client). In production, register LdClient as a singleton in DI instead of creating one per request.

Includes: Minimal ASP.NET Core Program.cs–style sample. SDK key: LAUNCHDARKLY_SDK_KEY (Apply: environment configuration).

using LaunchDarkly.Sdk;
using LaunchDarkly.Sdk.Server;

var builder = WebApplication.CreateBuilder(args);

var sdkKey = Environment.GetEnvironmentVariable("LAUNCHDARKLY_SDK_KEY");
if (string.IsNullOrWhiteSpace(sdkKey))
{
    Console.Error.WriteLine(
        "LAUNCHDARKLY_SDK_KEY is not set. Use Project settings > Environments > SDK key.");
    Environment.Exit(1);
}

var ldConfig = Configuration.Builder(sdkKey)
    .StartWaitTime(TimeSpan.FromSeconds(5))
    .Build();

// Construct the client before Build() per LaunchDarkly docs.
using var ldClient = new LdClient(ldConfig);

var app = builder.Build();

if (!ldClient.Initialized)
{
    Console.Error.WriteLine("LaunchDarkly client did not initialize within StartWaitTime.");
    Environment.Exit(1);
}

// For onboarding only — events are normally flushed in the background.
ldClient.Flush();
Console.WriteLine("LaunchDarkly client ready.");

// app.MapGet(...);
app.Run();

Optional — observability (SDK 8.10+): After adding LaunchDarkly.Observability, follow the ObservabilityPlugin.Builder(builder.Services) example in Initialize the client inside Configuration.Builder’s Plugins chain.