How to find out the value of Hiera from the Puppet function?

Question

I need to write a function that will, in order to do the following, to read the value of a variable:

• Check if a specific facter variable exists. If not,
• Read the value of the variable from Hiera. If not,
• Use the default value.

I managed to do this in my Puppet script using this if condition.

# foo is read from (in order of preference): facter fact, hiera hash, hard coded value if $::foo == undef { $foo = hiera('foo', 'default_value') } else { $foo = $::foo } 

But I want to avoid repeating this if condition for every variable that I want to analyze in this way, and therefore thought about writing a new Puppet function of the format get_args('foo', 'default_value') , which will return me the value from

• fact of fact, if it exists,
• hiera variable or
• just return default_value .

I know that I can use lookupvar to read the fact from the ruby ​​function. How to read hiera variable from my ruby ​​Puppet function?

Answer 1

You can call certain functions using the function_ prefix.

You have already found the lookupvar function.

Putting it all together:

 module Puppet::Parser::Functions newfunction(:get_args, :type => :rvalue) do |args| # retrieve variable with the name of the first argument variable_value = lookupvar(args[0]) return variable_value if !variable_value.nil? # otherwise, defer to the hiera function function_hiera(args) end end