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Getting Started with the OpenFeature PHP SDK on Laravel

Introduction​

This walk-through teaches you the basics of using OpenFeature with PHP using Laravel.

You'll learn how to:

  • Install the OpenFeature PHP SDK
  • Install and configure an OpenFeature provider
  • Perform basic feature flagging

Requirements​

This walk-through assumes that:

  • You should have a good understanding of PHP syntax, data types, operators, functions, and control structures.
  • You have PHP 8.0 or later.
  • You have Docker installed and running on the host system.

Walk-through​

Step 1: Create a new Laravel PHP project​

To get started, create a new folder, bootstrap the project, and install the dependencies. This can be done by running the following commands.

composer create-project --prefer-dist laravel/laravel openfeature-php-intro
cd openfeature-php-intro

Step 2: Create a sample response​

Define a route for your API by adding the following code to the routes/api.php file.

Route::get('/hello', function () {
    return response()->json(['message' => 'Hello, World!']);
});

Step 3: Add the OpenFeature SDK​

Let's install the OpenFeature SDK using the following command.

composer require open-feature/sdk

Update routes/api.php to import the SDK

use Illuminate\Http\Request;
use Illuminate\Support\Facades\Route;
use OpenFeature\OpenFeatureAPI;

The client can now be used to get a feature flag value. In this case, we'll get a boolean value using the welcome-message flag key.

The second argument is the fallback value, which is returned if there's abnormal behavior.

Route::get('/hello', function () {
    $api = OpenFeatureAPI::getInstance();
    $client = $api->getClient();
    if($client->getBooleanValue("welcome-message", false)){
        return response()->json(['message' => 'Hello, World! open feature']);
    }
    return response()->json(['message' => 'Hello, World!']);
});

Step 4: Run the application​

Let's start the app and see it in action. Run the following command to start the server.

php artisan serve

Open your favorite browser and navigate to http://localhost:8000/api/hello.

If all goes as planned, you should see the message "Hello, World!" in glorious monochrome.

"Why I'm I seeing that value?", you may ask. Well, it's because a provider hasn't been configured yet. Without a provider to actually evaluate flags, OpenFeature will return the default value. In the next step, you'll learn how to add a provider.

NOTE: You should stop the app by using the keyboard short ctrl + c before moving on to the next step.

Step 5: Configure a provider (flagd)​

Providers are an important concept in OpenFeature because they are responsible for the flag evaluation itself. As we saw in the previous step, OpenFeature without a provider always returns the default value. If we want to actually perform feature flagging, we'll need to register a provider.

Create a new file named flags.flagd.json and add the following JSON. Notice that there's a flag called welcome-message which matches the flag key referenced earlier. The welcome-message flag has on and off variants that return true and false respectively. The state property controls whether the feature flag is active or not. Finally, the defaultVariant property controls the variant that should be returned. In this case, the defaultVariant is off, therefore the value false would be returned.

{
  "flags": {
    "welcome-message": {
      "variants": {
        "on": true,
        "off": false
      },
      "state": "ENABLED",
      "defaultVariant": "off"
    }
  }
}

NOTE: This configuration is specific for flagd and varies across providers.

With the flagd configuration in place, start flagd service with the following docker command.

NOTE: On Windows WSL is required both for running docker and to store the file. This is a limitation of Docker (https://github.com/docker/for-win/issues/8479)

docker run -p 8013:8013 -v $(pwd)/:/etc/flagd/ -it ghcr.io/open-feature/flagd:latest start --uri file:/etc/flagd/flags.flagd.json

Also, we have to install PHP flagd provider. Open up your terminal and write this command.

composer require open-feature/flagd-provider

Now let's make the required code changes in our application.

Now, update routes/api.php to import the flagd provider.

use OpenFeature\OpenFeatureAPI;
use OpenFeature\Providers\Flagd\FlagdProvider;
use OpenFeature\Providers\Flagd\config\HttpConfig;
use GuzzleHttp\Client;
use GuzzleHttp\Psr7\HttpFactory;

Finally, we need to register the provider with OpenFeature.

Route::get('/hello', function () {
    $api = OpenFeatureAPI::getInstance();

    $httpClient = new Client();
    $httpFactory = new HttpFactory();
    $api->setProvider(new FlagdProvider([
        'httpConfig' => new HttpConfig(
            $httpClient,
            $httpFactory,
            $httpFactory,
        )
    ]));
    $client = $api->getClient();
    if($client->getBooleanValue("welcome-message", false)){
        return response()->json(['message' => 'Hello, World! open feature']);
    }
    return response()->json(['message' => 'Hello, World!']);
});

Step 6: Rerun the application​

Now that everything is in place, let's start the app again.

php artisan serve

Open your favorite browser and navigate to http://localhost:8000/api/hello should show the same value as before.

This difference is now the feature flag value can be changed at runtime!

Let's change the feature flag in our flags.flagd.json, making defaultVariant to on

{
  "flags": {
    "welcome-message": {
      "variants": {
        "on": true,
        "off": false
      },
      "state": "ENABLED",
      "defaultVariant": "off"
      "defaultVariant": "on"
    }
  }
}

Save the changes to flags.flagd.json and refresh the browser tab.

Conclusion​

This walk-through introduced you to the OpenFeature PHP SDK. It covered how a provider can be configured to perform the flag evaluation and introduced basic feature flagging concepts. It also showcased how feature flags can be updated at runtime, without requiring a redeployment.