Towards the Cloud: Event-driven Architectures in PHP

Event-Driven Architectures

Benjamin Eberlei

direkt effekt GmbH

IPC 09, Karlsruhe

Eberlei (direkt effekt GmbH) Event-Driven Architectures IPC 09, Karlsruhe 1 / 42

About Me

I Benjamin Eberlei

I direkt effekt GmBH

(digital marketing)

I Open Source contributor

(Zend Framework and Doctrine 2)

I Twitter @beberlei

I Blog: www.whitewashing.de


First: A typical monolithic PHPapplication


I Fowler, PoEAA: “Transaction Scripts”

I Retrieve Required Data from Database

I Process Data

I Make changes persistent

I Show the user some output

I Repeat.




I Process Data



I Repeat.




I Process Data



I Repeat.




I Process Data



I Repeat.




I Process Data



I Repeat.




I Process Data



I Repeat.


A Simple Application: PhotoCommunity


Photo

class Photo{

public $id;public $name;public $tags = array ();public $user = null;public $metadata = array ();public $originalFile = "";public $thumbnailFile = "";public $created = 0;

}


Tags and User

class User{

public $id;public $username;public $friends = array ();public $photos = array ();

}

class Tag{

public $id;public $name;public $photos = array ();

}


Photo Service

interface PhotoService{

function uploadRequestIsValid($post , $files);

function findOrCreateTags(array $tagNames);

function createPhoto($name , array $tags , User $user);

function saveToDb(Photo $photo);

function extractExifMetadata(Photo $photo);

function performResizes(Photo $photo);

function moveUploadedPhotoFile(Photo $photo , $file);

function notifyFriends(Photo $photo);}


Upload new Photo

$user = getSessionUser ();$service = new PhotoServiceImpl ();

if($service ->uploadRequestIsValid($_POST , $_FILES)) {// assign $tagNames , $name , $tempFile from Request

$tags = $service ->findOrCreateTags($tagNames);$photo = $service ->createPhoto($name , $tags , $user);

$service ->saveToDb($photo);

$service ->moveUploadedPhotoFile($photo , $tempFile);$service ->extractExifMetadata($photo);$service ->performResizes($photo);$service ->notifyFriends($photo);

}


Possible Problems

I Thumbnail generation

I View Caching

I CDN Distribution

I Payments/Credits

I Statistical Analysis

I Different Configurable Platforms


Possible Problems


I View Caching

I CDN Distribution

I Payments/Credits




Possible Problems


I View Caching

I CDN Distribution

I Payments/Credits




Possible Problems


I View Caching

I CDN Distribution

I Payments/Credits




Possible Problems


I View Caching

I CDN Distribution

I Payments/Credits




Possible Problems


I View Caching

I CDN Distribution

I Payments/Credits




You are always required to change thecore application!

1. Lots of Coupling.

2. Potential for great complexity.

3. Hard to maintain and test.

4. Not easily scaleable.


























Cronjobs to the Rescue?

I Put work in a queue

I Let a cronjob pick it up

I Or find work with a query

But:

I Not necessarily scaleable or decoupling.

I Single-Threaded

I Delayed by up to a minute






But:


I Single-Threaded







But:


I Single-Threaded







But:


I Single-Threaded







But:


I Single-Threaded







But:


I Single-Threaded




A software architecture where looslycoupled components communicate with

each other by triggering events.



1. Decouple responsibilities.

2. Communicate by triggering events.

3. Scale out components.

4. Higher responsiveness (Request MS

decrease).







decrease).







decrease).







decrease).


What is an Event?

“An event is a significantchange in state, which can betriggered from inside or outsidethe application.”

Wikipedia


What is an Event?


Uploading an Image


Patterns for Event-Driven Architectures


Subject-Observer Pattern #1



class PhotoUploader implements SplObserver{

function update(SplSubject $photo) {$this ->moveUploadedFile($photo);

}//...

}

class PhotoThumbGenerator implements SplObserver{

function update(SplSubject $photo) {$this ->performResizes($photo);

}//...

}

class PhotoMetadataExtractor implements SplObserver { }

class NewPhotoFriendsNotifier implements SplObserver { }



class Photo implements SplSubject{

private $observers = null;

function __construct () {$this ->observers = new SplObjectStorage ();$this ->attach(new PhotoUploader ());$this ->attach(new PhotoThumbGenerator ());$this ->attach(new PhotoMetadataExtractor ());$this ->attach(new NewPhotoFriendsNotifier ());

}

function notify () {foreach($this ->observers AS $observer) {

$observer ->update($this);}

}}



// $service instanceof PhotoServiceif($service ->uploadRequestIsValid($_POST , $_FILES)) {

// assign $tagNames , $name , $tempFile from Request


$service ->moveUploadedPhotoFile($photo , $tempFile);$service ->extractExifMetadata($photo);$service ->performResizes($photo);$service ->notifyFriends($photo);

$service ->saveToDb($photo);}



// $service instanceof PhotoServiceif($service ->uploadRequestIsValid($_POST , $_FILES)) {

// assign $tagNames , $name , $tempFile from Request


$photo ->notify ();

$service ->saveToDb($photo);}


Still too much coupling!


Event-Dispatcher Pattern #1

I Decouple Subject-Observer

I Introduce Event-Dispatcher Object

I Acts as Mediator between Subjects and

Observers

I Introduces Notion of a Channel






Observers







Observers







Observers






$dispatcher = new EventDispatcher ();$dispatcher ->attach("pre_save_photo", array(

new PhotoVirusScanner (),new PhotoIsValidImage (),

));$dispatcher ->attach("post_save_photo", array(

new PhotoThumbGenerator (),new PhotoCdnUploader (),new PhotoMetadataExtractor (),new NewPhotoFriendsNotifier ()

));



$user = getSessionUser ();$service = new PhotoServiceImpl ();// $service instanceof PhotoServiceif($service ->uploadRequestIsValid($_POST , $_FILES)) {

// assign $tagNames , $name , $tempFile from Request$tags = $service ->findOrCreateTags($tagNames);$photo = $service ->createPhoto($name , $tags , $user);

$dispatcher ->notify("pre_save_photo", $photo);

$service ->saveToDb($photo);

$dispatcher ->notify("post_save_photo", $photo);

}


Decoupled, Easily Maintainable andRe-Usable Components.

1. Photo, User, Tag Management

2. Photo Validator/Processor

3. Notification Mailer

4. Uploaded File Virus Scanning

5. File CDN Management


Attention!

Avoid using a shared Database


Open Questions

And how is this gonnasave me Request Time?


Open Questions

I know all this,what has this to do with the Cloud?


Asynchronous Processing


Message Systems for PHP

I XMPP

I dropr - https://www.dropr.org/

I Gearman - http://gearman.org/

I + lots of Java based ones


Gearman #1


Gearman #2

Installing on Linux is fairly easy already:root@benny -pc:~$ wget http:// launchpad.net/gearmand/trunk

/0.10/+ download/gearmand -0.10. tar.gzroot@benny -pc:~$ tar xzvf gearmand -0.10. tar.gzroot@benny -pc:~$ cd gearmand -0.10. tar.gzroot@benny -pc:~/ gearmand -0.10$ ./ configureroot@benny -pc:~/ gearmand -0.10$ makeroot@benny -pc:~/ gearmand -0.10$ make installroot@benny -pc:~/ gearmand -0.10$ ldconfigroot@benny -pc:~/ gearmand -0.10$ pecl install gearman -beta

Use packages daemonstools and

start-stop-daemon to manage workers and server

respectively.


PHP Gearman-Dispatcher

class GearmanEventDispatcher{

private $client;private $list = array();

function __construct () {$this ->client = new GearmanClient ();$this ->client ->addServer("127.0.0.1");

}

function notify($channel , $context) { }}


PHP Gearman-Dispatcher

class GearmanEventDispatcher{

function notify($channel , $context) {$contextData = serialize($context);foreach($this ->list[$channel] AS $listener) {

$listenerTaskName = $listener ->getTaskName ();if($listener ->isAsync ()) {

$this ->client ->doBackground($listenerTaskName , $contextData);

} else {$this ->client ->do(

$listenerTaskName , $contextData);}

}}

}


Gearman Worker

$uploader = new LoadUnserializer(new PhotoUploader ());$thumbGenerator = new LoadUnserializer(

new PhotoThumbGenerator ());

$worker= new GearmanWorker ();$worker ->addServer("127.0.0.1");$worker ->addFunction("upload_photo",

array($uploader , ’update ’));$worker ->addFunction("generate_thumb",

array($thumbGenerator , ’update ’));

while($worker ->work()) {// handle errors and return values here..

}


No need to stop here!

I We only looked at the model.

I Controller/View can also be an

Event-Dispatcher.

I Call several independant model

I Pre-calculate Ajax calls in main controller.

I Run your Test-Suite on several machines, in

parallel.

I Any more ideas?





Event-Dispatcher.




parallel.

I Any more ideas?





Event-Dispatcher.




parallel.

I Any more ideas?





Event-Dispatcher.




parallel.

I Any more ideas?





Event-Dispatcher.




parallel.

I Any more ideas?





Event-Dispatcher.




parallel.

I Any more ideas?


Further Readings

I “Enterprise Integration Patterns”, Hohpe, Woolf

I http://gearman.org/index.php?id=presentations

I http://www.php.net/gearman


Thank you!

Please rate this talk at joind.in:

http://joind.in/talk/view/1057

Twitter: @beberlei

Blog: www.whitewashing.de


Technology

Towards the Cloud: Event-driven Architectures in PHP