About Hiera

Puppet’s strength is in reusable code. Code that serves many needs must be configurable: put site-specific information in external configuration data files, rather than in the code itself.

Puppet uses Hiera to do two things:

• Store the configuration data in key-value pairs

• Look up what data a particular module needs for a given node during catalog compilation

This is done via:

• Automatic Parameter Lookup for classes included in the catalog

• Explicit lookup calls

Hiera’s hierarchical lookups follow a “defaults, with overrides” pattern, meaning you specify common data one time, and override it in situations where the default won’t work. Hiera uses Puppet’s facts to specify data sources, so you can structure your overrides to suit your infrastructure. While using facts for this purpose is common, data-sources can also be defined without the use of facts.

Puppet 5 comes with support for JSON, YAML, and EYAML files.

Related topics: Automatic Parameter Lookup.