lookup_key backends

A lookup_key backend function looks up a single key and returns its value. For example, the built-in hiera_eyaml backend is a lookup_key function.

You can view its source on Git at eyaml_lookup_key.rb.

Arguments

Hiera calls a lookup_key function with three arguments:

A key to look up.
A hash of options.
A Puppet::LookupContext object.

Return type

The function must either call the context object’s not_found method, or return a value for the requested key. It can return undef as a value.

Puppet language example signature:

function mymodule::hiera_backend(
  Variant[String, Numeric] $key,
  Hash                     $options,
  Puppet::LookupContext    $context,
)

Ruby example signature:

dispatch :hiera_backend do
  param 'Variant[String, Numeric]', :key
  param 'Hash', :options
  param 'Puppet::LookupContext', :context
end

A lookup_key function can return a hash for the the lookup_options key to configure merge behavior for other keys. See Configuring merge behavior in Hiera data for more information. To support Hiera interpolation tokens, for example, %{variable} or %{lookup('key')} in your data, call context.interpolate on your values before returning them.

Related information