Quickstart

The Eppo PHP SDK enables feature flags and experiments in your PHP applications with only a few lines of code.

Installation

Install the SDK using Composer:

composer require eppo/php-sdk

Initialize the SDK

Initialize the SDK with your SDK key:

use Eppo\EppoClient;

require __DIR__ . '/vendor/autoload.php';


$eppoClient = EppoClient::init(
   '<your_api_key>',
   '<base_url>', // optional, default https://fscdn.eppo.cloud/api
   $assignmentLogger, // optional, must be an instance of Eppo\Logger\LoggerInterface
   $cache // optional, must be an instance of PSR-16 SimpleCache\CacheInterface. If not passed, FileSystem cache will be used
   $httpClient // optional, must be an instance of PSR-18 ClientInterface. If not passed, Discovery will be used to find a suitable implementation
   $requestFactory // optional, must be an instance of PSR-17 Factory. If not passed, Discovery will be used to find a suitable implementation
);

Feature Flags

Make an Assignment

$subjectAttributes = [ 'tier' => 2 ];
$assignment = $eppoClient->getStringAssignment('experimentalBackground', 'user123', $subjectAttributes, 'control');

if ($assignment !== 'control') {
    // do something special
} else {
  // Show the default treatment
}

Experiments

For experiments, you'll need to implement logging. Here's a basic example:

<?php

use Eppo\Logger\LoggerInterface;

class Logger implements LoggerInterface {
  public function logAssignment(AssignmentEvent $assignmentEvent) {
    var_dump(assignmentEvent);
  }
}

Contextual Bandits

Contextual Multi-Armed Bandits are a way to dynamically optimize assignments based on user context. A bandit balances exploration of new actions with exploitation of known successful actions to maximize a specified metric.

Bandit Setup

Setting up a bandit requires two loggers:

1. An assignment logger (same as experiments)
2. A bandit logger for recording bandit-specific events

use Eppo\Logger\AssignmentEvent;
use Eppo\Logger\BanditActionEvent;
use Eppo\Logger\IBanditLogger;

class SegmentLogger implements IBanditLogger
{
    public function logAssignment(AssignmentEvent $assignmentEvent): void
    {
        Segment::track([
            'event' => 'Flag Assignment for ' . $assignmentEvent->featureFlag,
            'userId' => $assignmentEvent->subject,
            'properties' => $assignmentEvent->toArray()
        ]);
    }

    public function logBanditAction(BanditActionEvent $banditActionEvent): void
    {
        Segment::track([
            'event' => 'Bandit Action Selected',
            'userId' => $banditActionEvent->subjectKey,
            'properties' => $banditActionEvent->toArray()
        ]);
    }
}

Query the bandit for actions

Instead of making simple assignments with a bandit, you query the bandit for actions. The bandit considers both the subject context (like user attributes) and action contexts (like product attributes) when making decisions.

<?php

use Eppo\Logger\AssignmentEvent;
use Eppo\Logger\BanditActionEvent;
use Eppo\Logger\IBanditLogger;

class SegmentLogger implements IBanditLogger
{
    public function logAssignment(AssignmentEvent $assignmentEvent): void
    {
        Segment::track([
            'event' => 'Flag Assignment for ' . $assignmentEvent->featureFlag,
            'userId' => $assignmentEvent->subject,
            'properties' => $assignmentEvent->toArray()
        ]);
    }

    public function logBanditAction(BanditActionEvent $banditActionEvent): void
    {
        Segment::track([
            'event' => 'Bandit Action Selected',
            'userId' => $banditActionEvent->subjectKey,
            'properties' => $banditActionEvent->toArray()
        ]);
    }
}

The bandit will return both:

• A variation (indicating whether the subject is in the experiment)
• An action (the specific choice the bandit made, if the subject is in the experiment)

note

For full steps to create a bandit including UI steps, see the bandit quickstart.