Editing Quattor (section)

== Principles ==

The challenge of structuring and sharing components in a collaborative system is not new; over
the years programming language designers have attacked this problem from many angles. While
trends change, the basic principles are well understood. Features such as encapsulation, abstraction,
modularity, and typing produce clear benefits. We believe that similar principles apply when sharing
configuration information across administrative domains.

The Quattor configuration tool-kit derives its architecture from [[LCFG]], improving it in several
aspects. At the core of Quattor is Pan, a high-level, typed language with flexible include mechanisms,
a range of data structures, and validation features familiar to modern programmers. Pan
allows collaborative administrators to build up a complex set of configuration templates describing
service types, hardware components, configuration parameters, users etc. The use of a high-level
language facilitates code reuse in a way that goes beyond cut-and-paste of configuration snippets.

The principles embodied in Quattor are in line with those established within the system administration
community. In particular, all managed nodes retrieve their configurations from
a configuration server backed by a source-control system (or systems in the case of devolved management).
This allows individual nodes to be recreated in the case of hardware failure. Quattor
handles both distributed and traditional (single-site) infrastructures.

Devolved management includes the following features: consistency over a multi-site
infrastructure, multiple management points, and the ability to accommodate the specific needs
of constituent sites. There is no single “correct” model for a devolved infrastructure, thus great
flexibility is needed in the architecture of the configuration system itself. Sometimes a set of highly autonomous
sites wish to collaborate loosely. In this case each site will host a fairly comprehensive
set of configuration servers, with common configuration information being retrieved from a shared
database and integrated with the local configuration.

Distributing the management task can potentially introduce new costs. For example, transmitting
configuration information over the WAN introduces latency and security concerns. Quattor
allows servers to be placed at appropriate locations in the infrastructure to reduce latency, and
the use of standard tools and protocols means that existing security systems (such as a public key
infrastructure) can be harnessed to encrypt and authenticate communications.