LaunchDarkly OpenFeature provider for the Server-Side SDK for Node.js

This provider allows for using LaunchDarkly with the OpenFeature JS SDK.

This provider is designed primarily for use in multi-user systems such as web servers and applications. It follows the server-side LaunchDarkly model for multi-user contexts. It is not intended for use in desktop and embedded systems applications.

LaunchDarkly overview

LaunchDarkly is a feature management platform that serves trillions of feature flags daily to help teams build better software, faster. Get started using LaunchDarkly today!

Supported Node versions

This version of the LaunchDarkly OpenFeature provider is compatible with Node.js versions 18 and above.

Getting started

Installation

npm install @openfeature/server-sdk
npm install @launchdarkly/node-server-sdk
npm install @launchdarkly/openfeature-node-server

Usage

import { OpenFeature } from '@openfeature/server-sdk';
import { LaunchDarklyProvider } from '@launchdarkly/openfeature-node-server';

// The LaunchDarkly provider will use a 10 second timeout by default when waiting for the SDK
// to initialize. This can be controlled by the optional third parameter to the LaunchDarklyProvider
// constructor.
const ldProvider = new LaunchDarklyProvider('<your-sdk-key>', {/* LDOptions here */});

OpenFeature.setProvider(ldProvider);

// Alternatively await OpenFeature.setProviderAndWait(ldProvider); can be used.
// This eliminated the need to listen for the ready event, but the user should be careful to handle
// any exceptions that are thrown.

// If you need access to the LDClient, then you can use ldProvider.getClient()

// Evaluations before the provider indicates it is ready may get default values with a
// CLIENT_NOT_READY reason.
OpenFeature.addHandler(ProviderEvents.Ready, (eventDetails) => {
    const client = OpenFeature.getClient();
    const value = await client.getBooleanValue('app-enabled', false, {targetingKey: 'my-key'});
});

// The LaunchDarkly provider supports the ProviderEvents.ConfigurationChanged event.
// The provider will emit this event for any flag key that may have changed (each event will contain
// a single key in the `flagsChanged` field).
OpenFeature.addHandler(ProviderEvents.Ready, (eventDetails) => {
    console.log(`Changed ${eventDetails.flagsChanged}`);
});

// When the LaunchDarkly provider is closed it will flush the events on the LDClient instance.
// This can be useful for short lived processes.
await OpenFeature.close();

Refer to the SDK reference guide for instructions on getting started with using the SDK.

OpenFeature Specific Considerations

LaunchDarkly evaluates contexts, and it can either evaluate a single-context, or a multi-context. When using OpenFeature both single and multi-contexts must be encoded into a single EvaluationContext. This is accomplished by looking for an attribute named kind in the EvaluationContext.

There are 4 different scenarios related to the kind:

1. There is no kind attribute. In this case the provider will treat the context as a single context containing a "user" kind.
2. There is a kind attribute, and the value of that attribute is "multi". This will indicate to the provider that the context is a multi-context.
3. There is a kind attribute, and the value of that attribute is a string other than "multi". This will indicate to the provider a single context of the kind specified.
4. There is a kind attribute, and the attribute is not a string. In this case the value of the attribute will be discarded, and the context will be treated as a "user". An error message will be logged.

The kind attribute should be a string containing only contain ASCII letters, numbers, ., _ or -.

The OpenFeature specification allows for an optional targeting key, but LaunchDarkly requires a key for evaluation. A targeting key must be specified for each context being evaluated. It may be specified using either targetingKey, as it is in the OpenFeature specification, or key, which is the typical LaunchDarkly identifier for the targeting key. If a targetingKey and a key are specified, then the targetingKey will take precedence.

There are several other attributes which have special functionality within a single or multi-context.

• A key of privateAttributes. Must be an array of string values. Equivalent to '_meta.privateAttributes' in the SDK.
• A key of anonymous. Must be a boolean value. Equivalent to 'anonymous' in the SDK.
• A key of name. Must be a string. Equivalent to 'name' in the SDK.

Examples

A single user context

const evaluationContext = {
    targetingKey: 'my-user-key'
};

A single context of kind "organization"

const evaluationContext = {
    kind: 'organization',
    targetingKey: 'my-org-key'
};

A multi-context containing a "user" and an "organization"

const evaluationContext = {
    kind: 'multi',
    organization: {
        targetingKey: 'my-org-key',
        myCustomAttribute: 'myAttributeValue'
    },
    user: {
        targetingKey: 'my-user-key'
    }
};

Setting private attributes in a single context

const evaluationContext = {
    kind: 'organization',
    name: 'the-org-name',
    targetingKey: 'my-org-key',
    myCustomAttribute: 'myCustomValue',
    privateAttributes: ['myCustomAttribute']
};

Setting private attributes in a multi-context

const evaluationContext = {
    kind: 'multi',
    organization: {
        targetingKey: 'my-org-key',
        name: 'the-org-name',
        // This will ONLY apply to the "organization" attributes.
        privateAttributes: ['myCustomAttribute'],
        // This attribute will be private.
        myCustomAttribute: 'myAttributeValue'
    },
    user: {
        targetingKey: 'my-user-key',
        anonymous: true,
        // This attribute will not be private.
        myCustomAttribute: 'myAttributeValue'
    }
};

Learn more

Read our documentation for in-depth instructions on configuring and using LaunchDarkly. You can also head straight to the complete reference guide for this SDK.

The authoritative description of all properties and methods is in the TypeScript documentation.

Contributing

We encourage pull requests and other contributions from the community. Check out our contributing guidelines for instructions on how to contribute to this SDK.

About LaunchDarkly

• LaunchDarkly is a continuous delivery platform that provides feature flags as a service and allows developers to iterate quickly and safely. We allow you to easily flag your features and manage them from the LaunchDarkly dashboard. With LaunchDarkly, you can:
  • Roll out a new feature to a subset of your users (like a group of users who opt-in to a beta tester group), gathering feedback and bug reports from real-world use cases.
  • Gradually roll out a feature to an increasing percentage of users, and track the effect that the feature has on key metrics (for instance, how likely is a user to complete a purchase if they have feature A versus feature B?).
  • Turn off a feature that you realize is causing performance problems in production, without needing to re-deploy, or even restart the application with a changed configuration file.
  • Grant access to certain features based on user attributes, like payment plan (eg: users on the ‘gold’ plan get access to more features than users in the ‘silver’ plan). Disable parts of your application to facilitate maintenance, without taking everything offline.
• LaunchDarkly provides feature flag SDKs for a wide variety of languages and technologies. Check out our documentation for a complete list.
• Explore LaunchDarkly
  • launchdarkly.com for more information
  • docs.launchdarkly.com for our documentation and SDK reference guides
  • apidocs.launchdarkly.com for our API documentation
  • blog.launchdarkly.com for the latest product updates