The Problem

Some ecommerce site

• reseller
• sell from multiple supplier
• customer order -> report back
• send orders to (multiple) remote APIs

Source: http://www.hongkiat.com/blog/common-http-errors/

Common issues...

• uploading an image fails or takes too long
• placing order fails or takes too long
• page loading takes too long

...and their causes

• improper error handling
• badly scaled application
• too much responsibilities on the frontend

Background processing...

• runs in the background
• runs without user interaction
• (does not block the "foreground" process)

Definition

Parallel execution

• run multiple actions in parallel
• might block the "foreground" process
• eg. multi-threading

Deferred execution

• run multiple actions
• different place/time/environment
• the result of execution is not important for the original process
• eg. job queues

Cron jobs

Deferred execution FTW

• removes responsibilities from the frontend
• may include retry strategy
• improves scalability

...in PHP

Parallel execution

Multi-threading: pthreads

• usual PHP builds are not thread-safe
• many PHP extensions are not thread-safe

https://redd.it/1jo517

Deferred execution

Job queues

• one or more queues
• one or more workers
• put the job in the queue and forget

Message Queues

• inter-process communication
• asynchronous
• operated by a message broker

Message Broker

• coordinates communication between parties
• validates/routes/transforms/stores messages
• ensures message delivery
• eg. Rabbit MQ, Apache ActiveMQ/Kafka

Publish/Subscribe pattern

• most common messaging pattern (in MQs)
• sender publishes the message
• message broker stores
• receiver subscribes for specific messages

Beanstalk

Golden rule

Replace the first character with "ph"

<?php

use Pheanstalk\Pheanstalk;


// Configuration
$pheanstalk = new Pheanstalk('127.0.0.1');


// Publisher

$pheanstalk
  ->useTube('order')
  ->put("order product #1234 from supplier #5");


// Subscriber

$job = $pheanstalk
  ->watch('order')
  ->reserve();


// Process order
$data = $job->getData();


// Delete job from the queue
$pheanstalk->delete($job);

Bernard

• MQ abstraction
• supports the major ones
• https://github.com/bernardphp/bernard

<?php

// Configuration
$producer = ...;
$consumer = ...;
$queue = ...;


// Publisher (== producer)
$producer->produce(
    new Message\DefaultMessage('Order', [
        'product_id' => 1234,
        'supplier_id' => 5,
    ]),
    $queue->getName()
);


// Subscriber (== consumer)
$consumer->consume($queue);

Command pattern

• message
• information about an action to be executed
• no return value, but can trigger events
• improves testability

Tactician

• simple command bus implementation
• uses middlewares internally
• maintained by The League (Ross Tuck)
• http://tactician.thephpleague.com

<?php

declare(strict_types=1);

final class Order
{
    private $productId;
    private $supplierId;

    public function __construct(int $productId, int $supplierId)
    {
        $this->productId = $productId;
        $this->supplierId = $supplierId;
    }

    public function getProductId() : int
    {
        return $this->productId;
    }


    public function getSupplierId() : int
    {
        return $this->supplierId;
    }
}

final class OrderHandler
{
    // some dependencies

    public function handle(Order $command)
    {
        // do something
    }
}

<?php

// Configuration
$commandBus = ...;
$consumer = ...;
$queue = ...;


// Producer
$command = new Order(1234, 5);

$commandBus->handle($command);


// Consumer
$consumer->consume($queue);