Tools for server clusters in PHP

Learn how to create multiprocess server clusters.


This package provides tools to run multiple PHP processes that can listen on the same port, such as multiple HTTP server instances listening on the same port. Port-sharing is achieved with SO_REUSEPORT where available and socket transfers otherwise.

Additionally, this package provides a mechanism to gracefully restart such processes with zero downtime. The entire cluster may be manually restarted or failed workers will automatically be respawned by the cluster watcher process.

Instead of starting the processes with php server.php, cluster-enabled applications are started with php vendor/bin/cluster server.php.

A graceful restart can be initiated by sending a USR1 signal to the cluster process.

Cluster-enabled applications need only replace a few components with those provided by this package.

Creating a Server

Amp\Socket\Server::listen() is usually used to create an instance of Amp\Socket\Server for accepting client connections.

Instead, Amp\Cluster\Cluster::listen() returns a promise that resolves to an instance of Amp\Socket\Server. Cluster::listen() allows addresses and ports to be shared across multiple PHP processes (or threads).


Log entries may be send to the cluster watcher to be logged to a single stream by using Amp\Cluster\Cluster::createLogHandler(). This handler can be attached to a Monolog\Logger instance.

Process Termination

Often signals are used to gracefully shutdown a server when a SIGTERM signal is received by the process. Instead of Amp\Loop::onSignal(), cluster-enable applications should use Amp\Cluster\Cluster::onTerminate() to define functions that handle graceful shutdown when SIGINT or SIGTERM is received.

Hot Reload in IntelliJ / PHPStorm

IntelliJ’s file watchers can be used as trigger to send the USR1 signal to the cluster’s watcher process automatically on every file save. You need to write a PID file using --pid-file /path/to/ when starting the cluster and then setup a file watcher in the settings using the following settings:

  • Program: bash
  • Arguments: -c "if test -f ~/; then kill -10 $(cat ~/; fi"

Example HTTP Server

The example below (which can be found in the examples directory as simple-http-server.php) uses amphp/http-server to create an HTTP server that can be run in any number of processes simultaneously.


require \dirname(__DIR__) . "/vendor/autoload.php";

// This example requires amphp/http-server to be installed.

use Amp\ByteStream;
use Amp\Cluster\Cluster;
use Amp\Http\Server\Request;
use Amp\Http\Server\RequestHandler\CallableRequestHandler;
use Amp\Http\Server\Response;
use Amp\Http\Server\Server;
use Amp\Http\Status;
use Amp\Log\ConsoleFormatter;
use Amp\Log\StreamHandler;
use Amp\Promise;
use Monolog\Logger;

// Run using bin/cluster examples/simple-http-server.php
// Test using your browser by connecting to http://localhost:8080/

Amp\Loop::run(function () {
    // Create socket servers using the Cluster::listen() method to share ports across processes.
    // Cluster::listen() returns a promise, so yield the array to wait for all promises to resolve.
    $sockets = yield [

    // Creating a log handler in this way allows the script to be run in a cluster or standalone.
    if (Cluster::isWorker()) {
        $handler = Cluster::createLogHandler();
    } else {
        $handler = new StreamHandler(ByteStream\getStdout());
        $handler->setFormatter(new ConsoleFormatter);

    $logger = new Logger('worker-' . Cluster::getContextId());

    // Set up a simple request handler.
    $server = new Server($sockets, new CallableRequestHandler(function (Request $request): Response {
        return new Response(Status::OK, [
            "content-type" => "text/plain; charset=utf-8"
        ], "Hello, World!");
    }), $logger);

    // Start the HTTP server
    yield $server->start();

    // Stop the server when the worker is terminated.
    Cluster::onTerminate(function () use ($server): Promise {
        return $server->stop();