How to scale PHP applications

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 © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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 A Google server ● We need load balancers to split the traffic between all the servers © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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) © All rights reserved. Zend Technologies, Inc.

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"; © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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) © All rights reserved. Zend Technologies, Inc.

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/ © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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! © All rights reserved. Zend Technologies, Inc.

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. © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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 © All rights reserved. Zend Technologies, Inc.

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How to scale PHP applications

by Enrico Zimuel

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