FeatureFlagBundle

Easily toggle features in your Symfony app. Built-in providers are .env, cookies and userAgent. But you can extend the system with own providers (f.e. for A/B testing).

Install

Install the package via composer:

composer require check24/feature-flag-bundle

Usage

Accessing feature flag states

Limit access to controller actions

You can use the IsActive annotation to let the action only be accessible if the given feature is active. Otherwise a 403 is thrown:

use Shopping\FeatureFlagBundle\Annotation\IsActive;

/**
 * @Route("test")
 * @IsActive("foobar")
 * @return Response
 */
public function test(): Response
{
    return new Response('I can see you.');
}

As a dependency injection

To access the state of a feature inside a service, you can inject the FeatureFlagInterface

use Shopping\FeatureFlagBundle\Service\FeatureFlagInterface;

class SomeService
{
    private $featureFlag;

    public function __construct(FeatureFlagInterface $featureFlag)
    {
        $this->featureFlag = $featureFlag;
    }

    public function getNumber(): int
    {
        if ($this->featureFlag->isActive('foobar')) {
            return 2;
        }

        return 1;
    }
}

In Twig

Use the twig function is_active to check if a feature is enabled:

{% if is_active('foobar') %}
    Awesome!
{% else %}
    Default...
{% endif %}

Configuring feature flag providers

In your config/packages/shopping_feature_flag.yaml configuration, you can configure the built-in providers to define, which feature flag (key) should be active, when the user inputs on of the values:

shopping_feature_flag:
    providers:
        cookie:
            values:
                test1: 1234
                test2: [5678,9999]
        userAgent:
            values:
                test: foobar/chrome
                test2: [foobar/chrome, foobar/firefox]

You can enable/disable some of the built in providers.

Toggling features

Feature flags can be toggled by the configured providers. If at least one of the providers reports the feature as active, it is active.

.env

Toggle a feature environment wide in your .env file. You could f.e. disable the feature in your productive .env file but enable it in your staging .env file.

FEATUREFLAG_FOOBAR=1

(Prefix "FEATUREFLAG_" and uppercase feature flag name)

Cookie

Activate a feature only for yourself by setting a cookie in your browser, f.e. in Chrome with F12 -> Application -> Cookies

featureFlag_foobar=1

(Prefix "featureFlag_" and feature flag name)

If you haven't specified a specific value in the config for the feature flag, any value will activate the feature. Use the config to make the features more secure.

User-Agent

Activate a feature only for yourself by setting a custom User-Agent in your browser (f.e. with the Chrome plugin "User-Agent Switcher").

Configure in the shopping_feature_flag.yaml, what parts of the User-Agent activates what feature:

shopping_feature_flag:
    providers:
        userAgent:
            values:
                foobar: foobar/chrome

-> When using a User-Agent containing the string foobar/chrome, the Feature "foobar" is active. This way it is possible to activate multiple features with one User-Agent, which contains all needed keys for the features while preserving the browser/device detection of the website.

Create own provider

If you want to activate features in a custom way, you want to write your own provider.

In this example we create a time-based provider, so the specific feature "morningShow" is only activated between 8 and 10 a.m. .

First create a provider class, implement the FeatureFlagInterface with the isActive() method. This method should return true if the given feature is active. Otherwise return false.

//src/FeatureFlagProvider/MorningProvider.php

namespace App\FeatureFlagProvider;

class MorningProvider implements FeatureFlagInterface
{
    /**
     * @param string $featureFlag
     *
     * @return bool
     */
    public function isActive(string $featureFlag): bool
    {
        if ($featureFlag !== 'morningShow') {
            return false;
        }

        $hour = (new \DateTime())->format('G');

        return $hour >= 8 && $hour <= 10;
    }
}

Remember: A feature is active if any provider reports it as being active, so returning false doesn't deactivate the feature completely, but instead looks into all other providers if they report it as active.

Next, tag the service with the featureFlag.provider tag:

# config/services.yaml

services:
    App\FeatureFlagProvider\MorningProvider:
        tags:
            - { name: featureFlag.provider }

And you are done. The feature "morningShow" will now always be active between 8 and 10 a.m.

You can use this feature to realise an A/B testing, so you activate the feature only for a specific group of users.

Env Var Processor

To use a feature flag's value within a bundle's configuration you may use the feature_flag env var processor. This is especially useful when used in conjunction with custom feature flag providers, f.e. when you're loading flags from a database via doctrine.

# config/packages/example_foo_bundle.yaml
example_foo_bundle:
    enable_baz: '%env(feature_flag:foo_bar)%'

The above snippet will set the enable_baz config of ExampleBundle to the value of a feature flag called foo_bar. You can use the same technique when you'd like to register a specific feature flag as container parameter:

# config/services.yaml

parameters:
    maintenance_mode: '%env(feature_flag:maintenance_mode)%'

$container->getParameter('maintenance_mode') will now contain either true or false, depending on whether the feature flag is active or not.