A YAML DSL for creating resources, classes etc using just Hiera
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README.md

What?

An experiment to see how Puppet would be without any branches, language, boolean logic, variables or scope, or weird ordering.

Achieve this by expressing classes and resources in YAML files. Everything is managed by hiera which means every property of every resource and class can be manipulated by the hierarchy of data.

Main features to consider are:

  • Everything is YAML - but normal Puppet classes are usable
  • No branching, variables or logic, hierarchy based overrides instead
  • Everything including every property of every resource can be managed by hiera
  • Resources are added in a top down manner
  • In any resource name or string value of any property ${foo} does hiera('foo')

With the hirarchy supplying data and any data, properties, classes and resource names being overridable there is no very little reason for branching or loops - which Puppet doesn't do anyway.

NOTE:: This is at best an exploration of the idea and not intended for every day use. The code was written on a plane mostly around 2am so it's pretty grim, but it's functional and a good way to explore how such a thing would feel

Why?

This is not ment as a replacement for the Puppet DSL, in fact you can use any existing Puppet Classes or Defines from this DSL - though you cannot do the overrides on those resources not created in the DSL.

I wanted to explore the possiblity of creating an entirely new experience ontop of the Puppet catalog, resources, providers etc that relies heavily on convention and not on any programming

As the input is all data this creates many oppertunities like creating UIs that generate this data dynamically, consider this an ENC on steriods. You can create resources and classes at will with relationships between those classes.

I can imagine versioned classes, or classes that require signoff before release to the estate or general workflows, simply because all you need is a database and something to provide the data to hiera, how you get there is up to you.

A possible use case for something like this would be a scenario Puppet module authors write good traditional Puppet modules but the less programming-inclined team members can use a system like this to use those modules without any programming knowledge.

Example?

First we start with a class, this is just classes/common.yaml:

resources:
  - notify:
    - starting

  - file:
    - /tmp/foo:
        content: hello

    - /tmp/bar:
        content: bar

  - notify:
    - ending:
        notify: Class[x]

  - class:
    - x

This class has a bunch of resources in it - it also includes another class x from normal puppet manifests.

The resources will be added in a way that means they get applied to the node top down in the order they appear here.

Now lets see how the hierarchy build up the resources and nodes:

Given a hiera config:

:backends:
  - yaml

:hierarchy:
  - "%{::fqdn}"
  - common

You can see we have a common and fqdn tier, lets look at the common tier:

classes:
  - common -> apache

It says it wants to include 2 classes common and apache but it also sets some ordering, the apache class will depend on the common class. Without ordering it would just be an array with 2 items, 1 per class.

Now lets look at the node specific YAML file:

classes:
  - apache -> webapp

notify::starting:
  message: start for country ${country}

notify::ending:
  message: ending overriden

x::y: hello

country: uk

Here we add a 3rd class called webapp which should depend on the apache class.

We override the message property of the Notify[starting] and Notify[ending] resources that were defined in the common class earlier.

Note the override for the Notify[starting] resource has a ${country} string in it which will be looked up in hiera - in this case this gets replaced with the string uk

And finally we supply the y parameter to the parameterized class x

Now you just need to activate these nodes in Puppet:

node default {
  hiera_node()
}

Output?

There is a fully worked example in hieradata and puppet_test.pp which produce the following output:

  start for country uk
  /Stage[main]/Common/Notify[starting]/message: defined 'message' as 'start for country uk'
  ending overriden
  /Stage[main]/Common/Notify[ending]/message: defined 'message' as 'ending overriden'
  /Stage[main]/X/Exec[/bin/echo 'inside x y is hello']: Triggered 'refresh' from 1 events
  Finished catalog run in 0.38 seconds