Cloudflare SDK reference

Overview

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

The Cloudflare SDK is designed to be used with one of the LaunchDarkly client-side SDKs as follows:

• The Cloudflare SDK gets all flags at the edge for a given context, and bootstraps them onto a cached payload
• The client-side SDK initializes the bootstrapped payload
• The client-side SDK evaluates the flags and sends events back to LaunchDarkly

If you are using Cloudflare SDK version 2.3.0 or later, then the Cloudflare SDK can send events back to LaunchDarkly directly. Using a client-side SDK is not necessary. You do need to configure the SDK to enable sending events. To learn more, read Configuration.

The Cloudflare SDK uses the Cloudflare KV as a persistent feature store, without connecting to LaunchDarkly for each flag evaluation. The Cloudflare SDK uses the flag configuration in the Cloudflare KV to evaluate flags. The latency for this evaluation is similar to the latency for any other request to the Cloudflare KV, that is, extremely low. LaunchDarkly sends flag configuration changes to the Cloudflare KV as they occur.

If you are using Cloudflare SDK version 2.3.0 or later, then the Cloudflare SDK does send events back to LaunchDarkly if you configure it to do so. To learn more, read Configuration.

Get started

After you configure the Cloudflare integration process in an existing project, follow these instructions to start using the LaunchDarkly SDK in your Cloudflare Worker:

• Install the SDK
• Initialize the client
• Evaluate a flag

Install the SDK

First, install the LaunchDarkly SDK as a dependency in your application using your application's dependency manager.

Here's how:

yarn add @launchdarkly/cloudflare-server-sdk
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Then turn on the Node.js compatibility flag in your wrangler.toml to allow the SDK to use node:events. Specify a build command in your wrangler.toml to use a bundler. Using a bundler to build your edge worker is recommended by Cloudflare.

compatibility_flags = [ "nodejs_compat" ]
[build]
command = "node build.js"
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Next, import the LaunchDarkly client in your application code:

import { init } from '@launchdarkly/cloudflare-server-sdk';
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Initialize the client

After you install and import the SDK, create an instance of LDClient. Specify your client-side ID and Cloudflare KV namespace here. The client-side ID is only used to query the KV namespace, not to connect with LaunchDarkly servers.

Here's how:

const client = init('client-side-id-123abc', env.LD_KV);
await client.waitForInitialization();
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If you are using the Cloudflare SDK version 2.3.0 or later, you can optionally configure sending events during initialization. This enables Experimentation and metrics use cases. To learn more, read Experimentation and metric events.

Here's how:

const client = init('client-side-id-123abc', env.LD_KV, { sendEvents: true });
await client.waitForInitialization();
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Evaluate a flag

Await the waitForInitialization function after you initialize the client. When waitForInitialization is resolved the client can serve feature flags.

Using client, you can check which variation a particular context will receive for a given feature flag. In your Cloudflare Worker application, place the client.variation code so that it is invoked as needed.

Here is an example:

const context = {
   "kind": 'user',
   "key": 'user-key-123abc',
   "name": 'Sandy'
};
const flagValue = await client.variation('flag-key-123abc', context, false);
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Example Worker

This is an example Cloudflare Worker application that initializes the ldClient and evaluates a feature flag for a context:

import { init } from '@launchdarkly/cloudflare-server-sdk';
export default {
  async fetch(request: Request, env: Bindings): Promise<Response> {
    const context = { kind: 'user', key: 'test-user-key-1' };
    // init the ldClient, wait and finally evaluate
    const client = init('client-side-id-123abc', env.LD_KV);
    await client.waitForInitialization();
    const flagValue = await client.variation('flag-key', context, false);
    return new Response(`${flagValue}`);
  },
};
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Read the full example in GitHub.

Promises and async

All asynchronous SDK methods that return a Promise are compatible with then/catch or async/await. You can use either.

Shut down the client

If you send events, you must flush those events before your worker exits to ensure that they are sent back to LaunchDarkly. To learn more, read Flushing events.

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

Supported features

• Anonymous contexts and users
• Configuration, including
  • Migration configuration
• Context configuration
• Evaluating flags
• Flag evaluation reasons
• Flushing events
• Getting all flags
• Logging configuration
• Migrations
• Secure mode
• Sending custom events
• Shutting down

Use in Cloudflare Workers only

This SDK is intended only for use in multi-user Cloudflare Workers only. Choose one of the other JavaScript-based SDKs for browser, server, or mobile environments.

Client-side browser environments:

• For React applications, read the React Web SDK reference.
• For Vue applications, read the Vue SDK reference.
• For all other client-side browser JavaScript applications, read the JavaScript SDK reference.

Non-browser environments:

• For server-side Node applications, read the Node.js SDK reference (server-side).
• For client-side Node applications, read the Node.js SDK reference (client-side).
• For React Native mobile applications read the React Native SDK reference.
• For Electron desktop applications, read the Electron SDK reference.

To learn more about LaunchDarkly's different SDK types, read Client-side, server-side, and edge SDKs.