Revamped cluster index #

The cluster index mechanism has been almost completely rewritten in Exponential 4.7.

Previous structure #

Up until Exponential 4.6, serving of binary files was done through several files:

• a custom index_cluster.php (default name), that contained setup specific configuration constants
• the file index_image.php, included from index_cluster.php, that included index_image_<specificbackend>.php
• the index_image_<specificbackend>.php file, that actually contained the logic to serve the files

This structure was confusing, and added quite a few files at root level, something we are trying to avoid

Revamped structure #

A unique file can now be found at document root level: index_cluster.php. This file will be the one serving binary files, and must be the rewrite target.

Depending on the configuration (see below), this file will use a gateway class, specific to each cluster backend, that can be found in kernel/clustering. Custom cluster index gateways can be added my means of extensions.

Configuration #

Configuration is now done through the already existing config.php. As always with this file, documentation can be found in the distributed config.php-RECOMMENDED file. For this rewrite, you will find about a dozen new constants, all prefixed with CLUSTER_. Optionaly, you can define those constants in a config.cluster.php file (needs to be created). In that case, the constants will be only available for cluster environment.

Some of them are settings (database host, database, password, NFS path...), while some of them are flags that can be enabled/disabled.

New features #

While this change makes the code structure way cleaner, it also comes up with added benefits:

• eTag & IF-MODIFIED-SINCE header support
• HTTP RANGE support, to support partial downloads (only for DFS clusters)
• unified error & debug handling