Editing Quattor (section)

=== Pan language ===
The Pan language compiler panc sits at the core of the Quattor tool-kit. It compiles machine configurations
written in the [[pan (programming language)|Pan configuration language]] by system administrators and produces XML or JSON
files (profiles) that are easily consumed by Quattor clients. The Pan language itself has a simple,
declarative syntax that allows simultaneous definition of configuration information and an associated
schema. In this section, we focus only on the Pan features that are relevant to devolved
management of distributed sites: validation, configuration reuse, and modularization.

'''Validation'''. The extensive validation features in the Pan language maximize the probability of
finding configuration problems at compile time, minimizing costly clean-ups of deployed misconfiguration.
Pan enables system administrators to define atomic or compound types with associated
validation functions; when a part of the configuration schema is bound to a type, the declared
constraints are automatically enforced.

'''Configuration reuse'''. Pan allows identification and reuse of configuration information through
“structure templates.” These identify small, reusable chunks of Pan-level configuration information
which can be used whenever an administrator identifies an invariant (or nearly invariant) configuration
sub-tree.

'''Modularization'''. With respect to the original design, two new features have been developed
to promote modularization and large-scale reuse of configurations: the name-spacing and load-path
mechanisms.

A full site configuration typically consists of a large number of templates organized into directories
and subdirectories. The Pan template name-spacing mimics (and enforces) this organization
much as is done in the Java language. The name-space hierarchy is independent of the configuration
schema. The configuration schema is often organized by low-level services such as firewall settings
for ports, account generation, log rotation entries, [[cron]] entries, and the like. In contrast, the Pan
templates are usually organized based on other criteria like high-level services (web server, mail
server, etc.) or by responsible person/group.

The name-spacing allows various parts of the configuration to be separated and identified. To
effectively modularize part of the configuration for reuse, administrators must be able to import
the modules easily into a site's configuration and to customize them. Users of the Pan compiler
combine a load-path with the name-spacing to achieve this. The compiler uses the load-path to search
multiple root directories for particular, named templates; the first version found on the load-path
is the one that is used by the compiler. This allows modules to be kept in a pristine state while
allowing sites to override any particular template.

Further, module developers can also expose global variables to parameterize the module, permitting
a system administrator to use a module without having to understand the inner workings
of the module's templates.

Quattor Working Group (QWG) templates are used to configure grid [[middleware]] services.
The QWG templates use all of the features of Pan to allow distributed sites to share grid [[middleware]] expertise.