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Using Open Feature SDKs


OpenFeature provides a shared, standardized feature flagging client - an SDK - which can be plugged into various 3rd-party feature flagging providers. Whether you're using an open-source system or a commercial product, whether it's self-hosted or cloud-hosted, OpenFeature provides a consistent, unified API for developers to use feature flagging in their applications. Documentation

GO Feature Flag believes in Open-Source and standardization, this is the reason why we have decided not implementing any custom SDK and rely only on Open Feature.

To be compatible with Open Feature, GO Feature Flag is providing a lightweight self-hosted API server (called relay proxy) that is using the GO Feature Flag module internally. When the relay proxy is running in your infrastructure, you can use the Open Feature SDKs in combination with GO Feature Flag providers to evaluate your flags.

This schema is an overview on how Open Feature is working, you can have more information about all the concepts in the Open Feature documentation.

Create a feature flag configuration

Create a new YAML file containing your first flag configuration.

# only admins will eval to true
is-admin: true
not-admin: false
variation: not-admin
- name: check admin
query: admin eq true
variation: is-admin

This flag split users in 2 groups. Those who were configured with admin attribute set to true will resolve to the variation is-admin. Otherwise, they will resolve to variation not-admin.

Create a relay proxy configuration file

Create a new YAML file containing the configuration of your relay proxy.

listen: 1031
pollingInterval: 1000
startWithRetrieverError: false
kind: file
path: /goff/flag-config.goff.yaml
kind: log

Install the relay proxy

We will run the relay proxy locally to make the API available. The default port will be 1031.

# Launch the container
docker run \
-p 1031:1031 \
-v $(pwd)/flag-config.goff.yaml:/goff/flag-config.goff.yaml \
-v $(pwd)/goff-proxy.yaml:/goff/goff-proxy.yaml \

If you don't want to use docker to install the relay proxy you can follow the documentation.

Use Open Feature SDK

In this example we are using the javascript SDK, but it is still relevant for all the languages.

Install dependencies

npm i @openfeature/server-sdk @openfeature/go-feature-flag-provider

Init your Open Feature client

In your app initialization you have to create a client using the Open Feature SDK and initialize it.

const {OpenFeature} = require("@openfeature/server-sdk");
const {GoFeatureFlagProvider} = require("@openfeature/go-feature-flag-provider");

// init Open Feature SDK with GO Feature Flag provider
const goFeatureFlagProvider = new GoFeatureFlagProvider({
endpoint: 'http://localhost:1031/' // DNS of your instance of relay proxy
// Sets the default feature flag provider
// Gets the client that is bound to default provider
const featureFlagClient = OpenFeature.getClient();

Evaluate your flag

Now you can evaluate your flags anywhere in your code using this client.

// Context of your flag evaluation.
// With GO Feature Flag you MUST have a targetingKey that is a unique identifier of the user.
const userContext = {
targetingKey: '1d1b9238-2591-4a47-94cf-d2bc080892f1', // user unique identifier (mandatory)
firstname: 'john',
lastname: 'doe',
email: '',
admin: true, // this field is used in the targeting rule of the flag "flag-only-for-admin"
// ...

(async () => {
const adminFlag = await featureFlagClient.getBooleanValue('flag-only-for-admin', false, userContext);
if (adminFlag) {
// flag "flag-only-for-admin" is true for the user
console.log("new feature for admin!");
} else {
// flag "flag-only-for-admin" is false for the user
console.log("not an admin, no feature");

Try changing the admin attribute in the userContext from true to false to see different executions flows running.

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