How to scale PHP applications

by Jan Burkl, Enrico ZimuelZend Technologies

http://www.zend.comjan.burkl@zend.com, enrico@zend.com

30th October 2010 – PHP Barcelona Conference

About us

● Jan Burkl (jan.burkl@zend.com)

● Senior System Engineer at Zend Technologies in Stuttgart (Germany) since 2006

● Enrico Zimuel (enrico@zend.com)

● Senior Consultant & Architect at Zend Technologies in Milan (Italy) since 2008

● Blog on web dev't: http://www.zimuel.it/blog

Summary

● Scalability of a web application

● How to scale a PHP application

● PHP session management

● Sharing session data using:

▶ Network file system▶ Database▶ Memcached▶ Redis▶ Zend Server Cluster Manager

Scalability of a web application

Scalability: general definition

“Scalability is a desirable property of a system, a network, or a process, which indicates its ability to either handle growing amounts of work in a graceful manner or to be enlarged”

Source: Wikipedia

Scalability of a web application

A web application is scalable when is able to manage a growing traffic with additional resources (CPU, RAM) without software changes

Scale vertically vs. Scale horizontally

● Scale vertically (scale up)

▶ Add resources to a single node in a system▶ Enhance the server (more CPU, more RAM, etc)▶ High availability difficult to implement

● Scale horizontally (scale out)

▶ Add mores nodes to a system▶ More servers, distributing the load▶ High availability easy to implement

Scale up vs. Scale out

Scale up Scale out

The web scale out

● As Google taught, the best way to scale an high traffic web application is horizontally

● No expensive servers to scale horizontally

● We need load balancers to split the traffic between all the servers

A Google server

A typical load balancer architecture

Load Balancer

Web Servers

Internet

Firewall

How to scale a PHP application?

● The PHP application uses session/local data?

▶ Yes = we have to manage the session/local data across multiple servers

● Using a persistent load balancer● Share the session data

▶ No = we can scale very easy (stateless)● Most of the PHP applications are not stateless,

they use session data

Persistent load balancer

● A client request is assigned always to the same server (means same session/local data)

● Pros:

▶ No software architecture changes● Cons:

▶ No fault tolerant, if a server goes down the session data are lost!

▶ The load balancer is the bottleneck▶ The persistent load balancer are expensive

Share the session data

● Manage the session data across the servers

● Pros:

▶ Fault tolerant, if a server goes down the load balancer can user another server

▶ No bottleneck in the load balancer▶ The stateless load balancer are cheaper

● Cons:

▶ Software architecture changes

PHP session management

Sessions in PHP

● Session support in PHP consists of a way to preserve certain data across subsequent accesses

● To identify the subsequent accesses, from the same client, PHP uses a cookie variable (PHPSESSID)

▶ Example: PHPSESSID= tclq3an1ri8dsfiuo43845loo1

● By default, session data are stored in the file system of the server

● In PHP we manage the session data using the $_SESSION global variable

PHP session management

● Configure the PHP session management (php.ini directives):

▶ session.name

● name of the session cookie identifier (PHPSESSID by default)

▶ session.save_handler

● defines the name of the handler which is used for storing and retrieving data associated with a session (files by default).

▶ session.save_path

● defines the argument which is passed to the save handler (with files handler is the path to store the session data)

Example (PHP sessions using files)

● <?phpsession_start();$_SESSION['user']= 'enrico';

● In session folder (for instance, /tmp) the PHP creates a file named sess_fvi9r84f14sjel8r28o6aqspr2 (where fvi9r84f14sjel8r28o6aqspr2 is PHPSESSID) that contains:

user|s:6:"enrico";

Share session data

● How to share PHP sessions between multiple servers?

▶ Using a Network File System▶ Using a Database▶ Using Memcached▶ Using Redis▶ Using Zend Server Cluster Manager▶ etc

session_set_save_handler()

● You can write your PHP session handler using the session_set_save_handler():

bool session_set_save_handler (callback $open,callback $close,callback $read,callback $write,callback $destroy,callback $gc)

● More info: http://php.net/manual/en/function.session-set-save-handler.php

Session sharingusing NFS

Session sharing using NFS

● Use the default PHP session handler (session.session_handler= files)

● NFS to store the session data files (session.save_path= NFS folder)

● Pros:▶ No changes on the PHP side

● Cons:▶ Highly inefficient▶ Not designed for high read/write ratio▶ Performance problems and data corruptions

Session sharingusing Database

Session sharing using DB

● Use the user PHP session handler (session.session_handler= user)

● Use the session_set_save_handler() to implement your db session handler

● Which db?▶ MySQL

http://www.php.net/manual/en/function.session-set-save-handler.php#81761

▶ Ms SQL Server● http://www.zimuel.it/blog/?p=402

▶ PostgreSQL, Oracle, etc

Session sharing using DB (2)

● Pros:▶ Solves the scalability limitation▶ A lot of best practices available▶ Wide installation base▶ DB is (normally) available

● Cons:▶ Sessions have almost 1:1 read/write ratio▶ Connection overhead▶ Single point of failure▶ Performance bottleneck

Session sharingusing Memcached

Session sharing using Memcached

● Use the memcached PHP session handler (session.session_handler= memcache)

● Pros:▶ Native session handler▶ Very fast (works in RAM)▶ Can be clustered

● Cons:▶ No persistent data (it's a caching system)▶ Cyclic memory (data can be overwritten if the

memory is full)

Session sharingusing Redis

What is Redis?

● Redis is an open-source, networked, in-memory, persistent, journaled, key-value data store (NoSQL).

● It's similar to memcached but the dataset is not volatile

● Developed by: Salvatore Sanfilippo

● Sponsored by vmware

● http://code.google.com/p/redis/

Session sharing using Redis

● Different PHP extensions for Redis:

▶ Predis, http://github.com/nrk/predis/

▶ Rediska, http://rediska.geometria-lab.net/

▶ redis.php, http://github.com/antirez/redisdotphp

▶ PHPRedis!, http://github.com/owlient/phpredis

● Custom session handler for Redis:▶ http://github.com/ivanstojic/redis-session-php

Session sharing using Redis (2)

● Pros:

▶ Fast (works in RAM)▶ Reliable (master-slave replication)

● Cons:

▶ PHP Redis extensions are 0.x version▶ Custom PHP session handler▶ Not so scalable* (data are stored in RAM)▶ No High Availability* (master-slave limitation)

* but Redis developers are working on a Cluster version!

Session sharingusing Zend ServerCluster Manager

What is Zend Server and Cluster Manager?

● Zend Server is a complete, enterprise-ready Web Application Server for running and managing PHP applications that require a high level of reliability, performance and security on Linux, Windows or IBM i.

● Zend Server Cluster Manager (ZSCM) extends the benefits of Zend Server across large-scale PHP deployments.

● With ZSCM you can build a real PHP cluster stack.

Session sharing with ZSCM

● Session Clustering Extension

● Session Clustering Daemon (SCD)

● Storage backends: Disk / Memory

● Peer-to-peer protocol to communicate between nodes

● Session management with master-backup architecture

Zend Server Cluster Manager architecture

Load Balancer

Firewall

High availability: session cluster

High availability: session cluster (2)

Session cluster with ZSCM

● Pros:

▶ Very Fast▶ Reliable (data are stored in master-backup

servers)▶ High Availability▶ Scalable (session data are stored in all the

nodes of the cluster)▶ No changes to the PHP code

● Cons:

▶ You need Zend Server on each node of the cluster

Questions?

Thank you for attending!

More info:http://www.zend.comhttp://phpconference.es

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