Using Edge Config with LaunchDarkly

Learn how to use Edge Config with Vercel's LaunchDarkly integration.

This guide will help you get started with using Vercel's LaunchDarkly integration with Edge Config. This integration allows you to use Edge Config as a configuration source for your LaunchDarkly feature flags.

LaunchDarkly allows you to enable and disable feature flags dynamically, decoupling feature rollouts from deployments. The LaunchDarkly Edge Config integration enables you to evaluate flags at the edge without making network calls to LaunchDarkly.

The LaunchDarkly Edge Config integration is only available to Enterprise LaunchDarkly customers. However, you do not need to have a Vercel Enterprise account.

Prerequisites

Before using this integration, you should have:

The latest version of Vercel CLI. To check your version, use vercel --version. To install or update Vercel CLI, use:
```
pnpm i -g vercel@latest
```
A project. If you don't have one, you can run the following terminal commands to create a Next project:
```
pnpm i next
```
terminal
```
npx create-next-app@latest
```
A Vercel project. If you don't have one, see Creating a Project
An Edge Config. If you don't have one, follow the Edge Config quickstart
The Edge Config SDK:
```
pnpm i @vercel/edge-config
```

Set up the LaunchDarkly integration
Visit the LaunchDarkly page in the Integration Marketplace and select the Add Integration button. From the Integration dialog:
1. Select a Vercel team and project to connect the integration to
2. Log into LaunchDarkly
3. Select the Authorize button to allow the integration to access your LaunchDarkly account data
4. Name the integration, and select an existing Edge Config or create a new one
Get your client-side ID
To use the integration, you'll need your client-side ID from LaunchDarkly. Here's how to add it to your project:
1. Go to the settings page of your LaunchDarkly dashboard.
2. Select the LaunchDarkly project your integration is connected to
3. On the next page, copy the Client-side ID under the environment your integration is connected to (for example, Test or Production)
Now, you must add the value to your project as an Environment Variable:
1. Navigate to your Vercel dashboard and select the project you want to use LaunchDarkly with
2. Under the Settings tab, navigate to Environment Variables, and create an LD_CLIENT_SIDE_ID variable with the value of your client-side ID
See our Environment Variables docs to learn more.

Use the LaunchDarkly integration in your code

Open your project's code on your local machine and do the following:

Install LaunchDarkly's Vercel Server SDK:
```
pnpm i @launchdarkly/vercel-server-sdk
```
Use Vercel CLI to pull your Vercel project's environment variables:
```
vercel env pull
```

Finally, create a middleware.ts file at the root of your project. This file will configure Edge Middleware that redirects your site visitors from /homepage to /new-homepage based on a feature flag fetched from LaunchDarkly:

middleware.ts

import { init } from '@launchdarkly/vercel-server-sdk';
import { createClient } from '@vercel/edge-config';
 
const edgeConfigClient = createClient(process.env.EDGE_CONFIG!);
const launchDarklyClient = init('YOUR CLIENT-SIDE ID', edgeConfigClient);
 
export const config = {
  // Only run the middleware on the dashboard route
  matcher: '/homepage',
};
 
export default function middleware(request: Request): Response {
  await launchDarklyClient.initFromServerIfNeeded();
  const launchDarklyContext = { kind: 'org', key: 'my-org-key' };
  const showExperimentalHomepage = await launchDarklyClient.variation(
    'experimental-homepage',
    launchDarklyContext,
    true,
  );
 
  if (showExperimentalHomepage) {
    const url = new URL(request.url);
    url.pathname = '/new-homepage';
    return Response.redirect(url);
  }
}

Next steps

Now that you have set up the LaunchDarkly Edge Config integration, you can explore the following topics to learn more:

Last updated on March 4, 2025

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Using Edge Config with LaunchDarkly

Prerequisites

Set up the LaunchDarkly integration

Get your client-side ID

Use the LaunchDarkly integration in your code

Next steps