Clustering

Clustering lets several web servers serve one Exponential site. The files under var/ (uploaded images and files, and the content caches) are kept on a shared NFS mount, and their metadata in a database table, so every server sees the same files at the same moment. A single server does not need clustering, whatever its size.

File handlers in Exponential 6

file.ini [ClusteringSettings] FileHandler decides how Exponential reads and writes the files of var/:

• eZFSFileHandler (shipped default): What it does: plain files on the local disk; Use it for: one web server
• eZDFSFileHandler: What it does: files on a shared NFS mount, their metadata in the ezdfsfile table, caches copied to each server's own disk; Use it for: several web servers

The database file handler eZDBFileHandler (files stored as BLOBs in the database) and the experimental eZFS2FileHandler were removed before Exponential 6; their pages here are kept as history.

Metadata backends of the DFS handler

• eZDFSFileHandlerMySQLiBackend: Database: MySQL, MariaDB; Provided by: the kernel (default)
• eZDFSFileHandlerPostgresqlBackend: Database: PostgreSQL; Provided by: the package se7enxweb/ezpostgresqlcluster (Composer suggests it)
• eZDFSFileHandlerOracleBackend: Database: Oracle; Provided by: the ezoracle extension

SQLite cannot hold the metadata of a cluster, and it cannot be the site database of several web servers either.

What is clustered

• Clustered: images and their aliases, binary and media files, and the content-related caches (view cache, template-block cache, the expiry and other caches the kernel writes through the cluster handler).
• Not clustered: the code, templates, designs, settings, the compiled templates and the INI cache. Each server keeps its own var/ directory and its own copy of the code; only the mount is shared.

The pages of this section

• Setting it up for an eZDFSFileHandler: the steps, from the table to the rewrite rules
• Cluster configuration settings: every key of file.ini and config.php
• Cluster file handlers: the handlers and their history
• Maintenance: purging, consistency checks, cronjobs
• Reverting a cluster setup and Uninstalling an eZDFS cluster
• Historical: Setting it up for an eZDBFileHandler, Uninstalling an eZDB cluster

Related pages

• Clustering and shared storage (operations guide with a checklist)
• Clustering and high availability
• file.ini