> ## Documentation Index > Fetch the complete documentation index at: https://launchdarkly.com/docs/llms.txt > Use this file to discover all available pages before exploring further. # PHP SDK reference This topic documents how to get started with the PHP SDK, and links to reference information on all of the supported features. **SDK quick links** LaunchDarkly's SDKs are open source. In addition to this reference guide, we provide source, API reference documentation, and a sample application:
Resource Location
SDK API documentation [SDK API docs](https://launchdarkly.github.io/php-server-sdk/)
Supported SDK Versions [PHP SDK](/docs/sdk/concepts/supported-versions#php-sdk)
GitHub repository [php-server-sdk](https://github.com/launchdarkly/php-server-sdk)
Sample application [PHP](https://github.com/launchdarkly/hello-php)
[OpenFeature PHP](https://github.com/launchdarkly/hello-openfeature-php-server)
Published module [Packagist](https://packagist.org/packages/launchdarkly/server-sdk)
## Get started After you complete the [Getting Started process](/docs/home/getting-started), follow these instructions to start using the LaunchDarkly SDK in your PHP application. ### Understand version compatibility The LaunchDarkly PHP SDK, version 6.x and higher, is compatible with PHP 8.1 and higher. Starting with version 6.6, the LaunchDarkly PHP SDK also requires that the `apcu` extension is installed and enabled. The SDK uses the [APCu cache](https://www.php.net/manual/en/book.apcu.php) to help improve performance. If you are using older versions: * The LaunchDarkly PHP SDK, version 5.x, is compatible with PHP 8.0 and higher. * The LaunchDarkly PHP SDK, version 4.x, is compatible with PHP 7.3 and higher. * If you need compatibility with older versions of PHP, use version 3.x of the LaunchDarkly PHP SDK. ### Install the SDK The first step is to install [Composer](https://getcomposer.org/) and the LaunchDarkly SDK as a dependency in your application. Refer to the [SDK releases page](https://github.com/launchdarkly/php-server-sdk/releases) to identify the latest version if you want to depend on a specific version. To install Composer: ```bash title="Shell" lines wrap theme={null} php composer.phar require launchdarkly/server-sdk # In earlier versions, this was "launchdarkly/launchdarkly-php" ``` Then require Composer's autoloader: ```php title="PHP" lines wrap theme={null} require 'vendor/autoload.php'; ``` **The PHP SDK uses an SDK key** The PHP SDK uses an SDK key. Keys are specific to each project and environment. They are available on the **SDK keys** page under **Settings**. To learn more about key types, read [Keys](/docs/sdk/concepts/client-side-server-side#keys-and-credentials). ### Initialize the client After you install and import the SDK, create a single, shared instance of [`LDClient`](http://launchdarkly.github.io/php-server-sdk/classes/LaunchDarkly-LDClient.html). Specify your SDK key here to authorize your application to connect to a particular environment within LaunchDarkly. Only create one instance of `client`. Here's how: ```php title="PHP" lines wrap theme={null} $client = new LaunchDarkly\LDClient("YOUR_SDK_KEY"); ``` To learn more about the specific configuration options available in this SDK, read the SDK API documentation for the [`LDClient` constructor](http://launchdarkly.github.io/php-server-sdk/classes/LaunchDarkly-LDClient.html#method___construct). ### Evaluate a context You can use `$client` to check which variation a particular context will receive for a given feature flag. Here's how: ```php title="PHP" lines wrap theme={null} $context = LDContext::builder("example-context-key") ->name("Sandy") ->build(); if ($client->variation("your.flag.key", $context)) { // application code to show the feature } else { // the code to run if the feature is off } ``` In our [Getting Started guide](/docs/home/getting-started) we recommend that users shut down the LaunchDarkly client on application termination. This step does not exist in PHP because the PHP SDK does not maintain long-lived network connections nor an event queue. ## Fetch flags There are two distinct methods of integrating LaunchDarkly in a PHP environment: * [The Relay Proxy](/docs/sdk/relay-proxy) retrieves and stores flags in [Redis](/docs/sdk/features/storing-data/redis), [DynamoDB](/docs/sdk/features/storing-data/dynamodb), or [Consul](/docs/sdk/features/storing-data/consul). This is the recommended method. If you use synced segments or larger list-based segments, you can only use Redis or DynamoDB as a persistent store. * [Guzzle Cache Middleware](https://github.com/Kevinrob/guzzle-cache-middleware) requests and caches HTTP responses in an in-memory array. This is the default method. We strongly suggest using the Relay Proxy. Per-flag caching mode using Guzzle is only intended for low-throughput environments. ### Using the Relay Proxy PHP's shared-nothing architecture prevents LaunchDarkly from reusing the streaming API connection across requests. You can use PHP without the Relay Proxy, but we strongly recommend using the Relay Proxy in **daemon mode** if you are using PHP in a high-throughput setting. This makes the Relay Proxy receive feature flag updates. To learn more, read [Configuring SDKs to use different modes](/docs/sdk/relay-proxy/sdk-config#configuring-sdks-to-use-different-modes). ### Using Guzzle For the latest major version of the PHP SDK, use open-ended dependencies. For older versions, refer to your version's composer.json file. To require Guzzle as a dependency: ```php title="PHP" lines wrap theme={null} php composer.phar require "guzzlehttp/guzzle:^6.3.0" php composer.phar require "kevinrob/guzzle-cache-middleware:^1.4.0" ``` Guzzle is then used to fetch flags. You can persist your cache somewhere other than the default in-memory store, like Memcached or Redis. You can then specify your cache when initializing the client with the cache option: ```php title="PHP" lines wrap theme={null} $client = new LaunchDarkly\LDClient("YOUR_SDK_KEY", ["cache" => $cacheStorage]); ``` ## Supported features This SDK supports the following features: * [SDK configuration](/docs/sdk/features/config#php), including * [Application metadata configuration](/docs/sdk/features/app-config#php) * [Migration configuration](/docs/sdk/features/migration-config#php) * [Service endpoint configuration](/docs/sdk/features/service-endpoint-configuration#php) * [Anonymous contexts and users](/docs/sdk/features/anonymous#php) * [Big segments](/docs/sdk/features/big-segments#php) * [Context configuration](/docs/sdk/features/context-config#php) * [Flag variation evaluation](/docs/sdk/features/evaluating#php) * [Flag variation evaluation details](/docs/sdk/features/evaluation-reasons#php) * [Flushing events](/docs/sdk/features/flush#php) * [Getting all flags](/docs/sdk/features/all-flags#php) * [Hooks](/docs/sdk/features/hooks#php) * [Identifying and changing contexts](/docs/sdk/features/identify#php) * [Logging configuration](/docs/sdk/features/logging#php) * [Migrations](/docs/sdk/features/migrations#php) * [Offline mode](/docs/sdk/features/offline-mode#php) * [OpenTelemetry](/docs/sdk/features/opentelemetry-server-side#php) * [Private attributes](/docs/sdk/features/private-attributes#php) * [Reading flags from a file](/docs/sdk/features/flags-from-files#php) * [Relay Proxy configuration](/docs/sdk/features/relay-proxy-configuration) * [Using proxy mode](/docs/sdk/features/relay-proxy-configuration/proxy-mode#php) * [Using daemon mode](/docs/sdk/features/relay-proxy-configuration/daemon-mode#php) * [Secure mode](/docs/sdk/features/secure-mode#php) * [Tracking custom events](/docs/sdk/features/events#php) * [Storing data](/docs/sdk/features/storing-data#node-js-server-side) * [Test data sources](/docs/sdk/features/test-data-sources#php)