Editing Quattor (section)

=== Node configuration management ===

In Quattor, managed nodes handle their configuration process autonomously; all actions are initiated locally, once the configuration profile has been retrieved from the repository.
Each node has a set of configuration agents (components) that are each registered with a particular part of the configuration schema.
For example, the component that manages user accounts is registered with the path /software/components/accounts.
A dispatcher program running on the node performs an analysis of the freshly retrieved configuration for changes in the relevant sections, and triggers the appropriate components.
Run-time dependencies may be expressed in the node's profile, so that a partial order can be enforced on component execution.
For example, it is important that the user accounts component runs before the file creation component, to ensure that file ownership can be correctly specified.

By design, no control loop is provided for ensuring the correct execution of configuration components.
Site administrators typically use standard monitoring systems to detect and respond to
configuration failures. [[Nagios]] and Lemon are both being used at Quattor sites for this
purpose. In fact, Lemon has been developed in tandem with Quattor, and provides sensors to
detect failures in Quattor component execution.

While nodes normally update themselves automatically, administrators can configure the system
to disable automatic change deployment. This is crucial in a devolved system where the responsibilities
for, respectively, modifying and deploying the configuration may be separated. A typical
scenario is that top-level administrators manage the shared configuration of multiple remote sites
and local managers apply it according to their policies. For instance, software updates might be
scheduled at different times.