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How to scale PHP applications
by Jan Burkl, Enrico Zimuel
Zend Technologies
http://www.zend.com
jan.burkl@zend.com, enrico@zend.com
30th
October 2010 – PHP Barcelona Conference

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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

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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

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Scalability of a web
application

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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

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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

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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

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Scale up vs. Scale out
Scale up Scale out
vs.

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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

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A typical load balancer architecture
Load Balancer
Web Servers
Internet
Firewall

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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

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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

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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

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PHP session management

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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

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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)

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Example (PHP sessions using files)
● <?php
session_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";

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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

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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

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Session sharing
using NFS

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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

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Session sharing
using Database

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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

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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

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Session sharing
using Memcached

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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)

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Session sharing
using Redis

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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/

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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

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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!

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Session sharing
using Zend Server
Cluster Manager

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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.

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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

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Zend Server Cluster Manager architecture
Load Balancer
MySQL
Firewall

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High availability: session cluster

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High availability: session cluster (2)

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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

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Questions?

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Thank you for attending!
More info:
http://www.zend.com
http://phpconference.es