Multi tenant CMSes using php

Multi-tenanted CMSes (with some PHP)

What is “multi-tenant”?
One Codebase
Install once, maintain/upgrade that one instance
Many domain names
Many configurations
Each site has its own config file, detailing
Database details – separate tables per domain, or separate databases
Skin/Theme details
User-uploaded file locations

Why bother?
Cheaper
install one copy of software
all instance data, configs, etc., installed automatically or using a “point and click” installer
Easier to maintain and upgrade
fix in one place, fix everywhere. upgrade once, upgrade everywhere
conversely: bugs/errors are universal, so be careful
Less resources needed
less HD space, as only one software instance
bytecode caching (APC, etc) for just 1 CMS copy, thus less file-access

Who's doing it?
Joomla, Orchard, Drupal, etc
all have tutorials explaining how to do it (not built into core)
Wordpress
WordPress-MU so cool it was written into the core
Salesforce
Google Apps
Why is it not more prevalent in OSS?

The flow
Server checks domain name
Finds config associated with domain name
Sets site-specific variables such as db details, file locations, theme details

Finding the config
Different methods
WordPress MU uses one database
One table holds details of each domain
WP searches table to find ID of blog associated with domain name
Each blog's details kept in numbered tables in the same database (eg: wp_2_links, wp_23_links, etc)
KV-WebME uses multiple databases
Config found using sym-links in file-system
Each site's config kept in a separate directory on the filesystem

Proxy Config /home/webme /public_html/index.php /.private/config.php /sites.aliases/kvsites.ie /sites/kv-2-30/config.php

Proxy Config <?php $host=preg_replace( '/^www./', '', preg_replace( '/[^a-z0-9-.]/', '', strtolower( $_SERVER['HTTP_HOST'] ) ) ); $cfile='/home/webme/ sites.aliases /'.$host.'/config.php'; if (!file_exists($cfile)) { $cfile='/home/webme/ sites /'.$host.'/config.php'; if (!file_exists($cfile)) { echo 'error resolving domain name "' .$_SERVER['HTTP_HOST'].'" to a WebME server'; exit; } } require $cfile; define('CONFIG_FILE', $cfile);

Files
Files are served through a router/proxy
mod_rewrite, nginx, etc
File's actual location determined by config file
URL is /file/whatever.jpg, but that's not where it really is
could be /home/webme/sites/kv-2-23/f/whatever.jpg

Flow for requesting a file
Get site's config directory
user-uploaded files kept in sub-directory (/home/webme/sites/kv-2-23/f)
Rewrite file requests to route through a script
RewriteRule ^f/(.*)$ /ww.incs/get-file.php?filename=$1 [L]
Retrieve actual file location
validate the filename, check that it exists
Push to client
readfile()

Advantages of proxied files
More secure
example: /f/whatever.php.jpg <-- image or script?
Authentication
require logged-in user, or that the user be a member of a certain group
Logging
record details such as what user viewed the file, push the file access to a live log view, etc.
Modification
if an image is /f/image.jpg , how about resizing it if called as /f/image.jpg,width=200

Managing Core Upgrades
Automate!
Keep version number of core database tables in config file.
Example: 'version'=>'32',
Hard-code version number into root /index.php
If versions don't match, run upgrade script, then re-save the config file with latest version
if (!isset($DBVARS['version']) || $DBVARS['version']<32 ) { redirect('/ww.incs/upgrade.php'); }

Managing New Installations
Run new installation from scratch
or...
Maintain a reference installation, and copy that one when creating new installation
Advantages
Skip lengthy upgrade cycles
Prepopulate with sample data
Customise

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Multi tenant CMSes using php

by kae-verens on Mar 18, 2011

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