How to Scale Php Application

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

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 webapplication

Scalability: general definition

“Scalability is a desirable property of asystem, a network, or a process, whichindicates its ability to either handlegrowing amounts of work in a gracefulmanner or to be enlarged”

Source: Wikipedia

Scalability of a web application

A web application is scalable when isable to manage a growing traffic withadditional 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 trafficweb application is horizontally

No expensive servers to scale horizontally

A Google server

We need load balancers to split the trafficbetween all the servers

A typical load balancer architecture

Load Balancer

Firewall

Internet

Web Servers

How to scale a PHP application?

The PHP application uses session/local data?

Yes = we have to manage the session/localdata 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 sameserver (means same session/local data)

● Pros:

No software architecture changes●Cons:

No fault tolerant, if a server goes down thesession 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 loadbalancer can user another server

No bottleneck in the load balancer

The stateless load balancer are cheaper●Cons:

Software architecture changes

Sessions in PHP

Session support in PHP consists of a way to preserve certaindata 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 theserver

In PHP we manage the session data using the $_SESSIONglobal variable

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 usedfor storing and retrieving data associated witha session (files by default).

session.save_path

defines the argument which is passed to thesave handler (with files handler is the path tostore the session data)

Example (PHP sessions using files)

<?phpsession_start();

$_SESSION['user']= 'enrico';

In session folder (for instance, /tmp) the PHP creates a filenamed sess_fvi9r84f14sjel8r28o6aqspr2 (wherefvi9r84f14sjel8r28o6aqspr2 is PHPSESSID) that contains:

user|s:6:"enrico";

Share session data

How to share PHP sessions between multipleservers?

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 usingthe 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 implementyour db session handler

Which db?▶MySQL

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

Ms SQL Serverhttp://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 thememory 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 thedataset is not volatile

Developed by: Salvatore Sanfilippo

How to Scale Php Application

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