Puppet - create NESTED custom fact

Question

I have successfully created a .rb custom fact that parses a built-in fact to create a new value, however I am now trying to use it as nested custom fact for Puppet.

The hierarchy I want to create is similar to built-in facts, eg running Facter (or Facter -p) would show:

custom_parent => {
  custom_fact_1 => whatever
  custom_fact_2 => whatever2
}

and usage in a puppet manifest would be:

$custom_parent.custom_fact_1

So far I have tried leading syntax such as:

Facter.add (:custom_parent)=>(custom_fact_1) do
Facter.add (:custom_parent)(:custom_fact_1) do
Facter.add (:custom_parent.custom_fact_1) do
Facter.add (:custom_parent:custom_fact_1) do
Facter.add (custom_parent:custom_fact_1) do

...and many other variations however cannot get a nested custom fact array to create. I've Googled for a while and if anyone knows if it is possible I would be very grateful.

I did find that nested facts can be created using an array in a .yaml file in the /etc/puppetlabs/facter/facts.d/ directory as below, however this sets FIXED values and does not process logic which I require in my custom fact.

{
  "custom_parent":
  {
    "custom_fact_1": "whatever",
    "custom_fact_2": "whatever2",
  }
}

Thanks in advance.

Documentation is here https://puppet.com/docs/facter/3.11/fact_overview.html#writing-structured-facts to the bottom of the page. If you want specific help for your fact, then we need to see your code. — Matthew Schuchard, Jun 24 '18 at 13:17

score 3 · Answer 1 · answered Jun 25 '18 at 20:20

The hierarchy I want to create is similar to built-in facts, eg running Facter (or Facter -p) would show:
custom_parent => {
  custom_fact_1 => whatever
  custom_fact_2 => whatever2
}

There are no "nested" facts. There are "structured" facts, however, and these may have hashes as their values. To the extent that Facter presents output that you characterize as "nested", that's surely what you're looking at.

Since the elements of a structured fact's value are not facts in their own right, they need to be specified in the resolution of the fact itself:

Facter.add (:custom_parent) do
    {
        :custom_fact_1 => 'whatever',
        :custom_fact_2 => 'whatever2',
    }
end

The whatever and whatever2 do not need to be literal strings; they can be more or less arbitrary Ruby expressions. Of course, you can also set the members separately from creating the hash (but in the same fact resolution):

Facter.add (:custom_parent) do
    value = new Hash()
    value[:custom_fact_1] = 'whatever'
    value[:custom_fact_2] = 'whatever2'
    value
end

Thank you @John Bollinger for examples and Matt Schuchard for pointing me to the correct page — xit, Jun 26 '18 at 09:56

xit · Accepted Answer · 2018-06-26T10:09:44.000

Thank you @John Bollinger. Your example was very close however I found that I needed to use type => aggregate and chunk to get it to work. I also combined it with a defined function, with the end result being based on the code below.

If you have any other suggestions to improve code conformity on this please feel free to point it out. Cheers

# define the function to process the input fact
def dhcp_octets(level)
  dhcp_split = Facter.value(:networking)['dhcp'].split('.')
  if dhcp_split[-level..-1]
    result = dhcp_split[-level..-1].join('.')
    result
  end
end

# create the parent fact
Facter.add(:network_dhcp_octets, :type => :aggregate) do
  chunk(:dhcp_ip) do
    value = {}

# return a child => subchild array
    value['child1'] = {'child2' => dhcp_octets(2)}

# return child facts based on array depth (right to left)
    value['1_octets'] = dhcp_octets(1)
    value['2_octets'] = dhcp_octets(2)
    value['3_octets'] = dhcp_octets(3)
    value['4_octets'] = dhcp_octets(4)

# this one should return an empty fact
    value['5_octets'] = dhcp_octets(5)
    value
  end
end

I'm glad you got it working. I assure you, however, that it was not necessary to implement this as an aggregate fact. Even if you did not accept my assurance as authoritative, the fact that your aggregate resolution has only one chunk demonstrates that it is so. — John Bollinger, Jun 26 '18 at 12:54
@JohnBollinger, you are correct. Initial testing only worked using aggregate, however once removed from the final code and 'chunk' replace with 'setcode do' it still functions as desired. The child facts do appear to need to be in single quotes however, not prepended with colon. Thanks again. — xit, Jun 27 '18 at 00:52

Puppet - create NESTED custom fact

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