Initialization

The Eppo PHP SDK is easy to initialize while offering robust customization options, making it adaptable to various use cases such as custom caching requirements and background polling, exposing PSR-6/17, PSR-17, and PSR-18 interfaces.

Initialize the SDK

To complete basic initialization, you only need to provide an SDK key. Create an SDK key if you don't already have one.

use Eppo\EppoClient;

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

$eppoClient = EppoClient::init("<your_sdk_key>");

Advanced Configuration

The SDK provides several optional parameters during initialization to customize its behavior:

Initialization Options

apiKeystringDefault: undefined

Your Eppo SDK key. Required for initialization.

baseUrlstringDefault: https://eppo.cloud/api

The base URL for the Eppo API.

assignmentLoggerLoggerInterfaceDefault: null

A callback that sends each assignment to your data warehouse. Required only for experiment analysis. Must implement the Eppo\Logger\LoggerInterface interface.

cacheCacheInterfaceDefault: FileSystem cache

A PSR-6 compatible cache implementation for storing flag configurations.

httpClientClientInterfaceDefault: automatic (Discovery)

A PSR-18 compatible client interface for making http requests.

requestFactoryRequestFactoryInterfaceDefault: automatic (Discovery)

A PSR-18 compatible client interface for making http requests.

Configuration Caching

The SDK can cache previously loaded configurations for use in future sessions. By default, it uses a filesystem cache, but you can provide your own PSR-6 compatible cache implementation:

use Symfony\Component\Cache\Adapter\RedisAdapter;

$cache = new RedisAdapter($redisConnection);

$eppoClient = EppoClient::init(
   "<your_sdk_key>",
   null,
   $assignmentLogger,
   $cache
);

Background Polling

A unique feature of the PHP SDK is its ability to poll for configuration updates in a background process. This ensures your application always has fresh configurations without blocking requests.

Create a dedicated poller file (e.g. eppo-poller.php):

$eppoClient = EppoClient::init(
   "<your_sdk_key>",
   "<base_url>",
   $assignmentLogger,
   $cache
);

$eppoClient->startPolling();

Run this as a separate process:

php eppo-poller.php

Assignment Logger

For experiment analysis, implement the LoggerInterface:

<?php

use Eppo\Logger\LoggerInterface;

class Logger implements LoggerInterface {
  public function logAssignment(AssignmentEvent $assignmentEvent) {
    // Implement your logging logic here
  }
}

The logger receives these parameters:

Field	Description	Example
experiment (string)	An Eppo experiment key	"recommendation-algo-allocation-17"
subject (string)	An identifier of the subject or user assigned to the experiment variation	UUID
variation (string)	The experiment variation the subject was assigned to	"control"
timestamp (string)	The time when the subject was assigned to the variation	2021-06-22T17:35:12.000Z
subjectAttributes (map)	A free-form map of metadata about the subject	{ "country": "US" }
featureFlag (string)	An Eppo feature flag key	"recommendation-algo"
allocation (string)	An Eppo allocation key	"allocation-17"
allocation (string)	An Eppo allocation key	"allocation-17"
sdkMetadata (map)	SDK version of other SDK metadata	{ "sdkName": "php", "sdkVersion": "1.0.0" }
extraLogging (map)	Freeform map of additional data to log	{"appVer":"5.0.9","cluster":"a4"}

note

More details about logging and examples (with Segment, Rudderstack, mParticle, and Snowplow) can be found in the event logging page.