Thursday, March 20, 2014

My first custom Puppet function in Ruby

Here the doc

I thought this was Rocket Science, but it's quite simple, once you overcome the normal, healthy, instinctive repugnance for a stinky stupid language like Ruby. Anyway if you are already coping with Puppet, Ruby should not be worse.

Inside your Puppet module, create these folders: lib/puppet/parser/functions, and inside your function file "stage_from_domain.rb" (file name should match the function name, and extension = .rb).

The file should start with a "module Puppet::Parser::Functions" declaration (no clue why... just to make your pronounce some meaningless magic words initiating you to the Puppet Mysteries - luckily they don't ask you to kill a kitten).

The function returns a substring in the middle of a string. Since we RETURN a value, we must declare it as ":type => :rvalue":
module Puppet::Parser::Functions
  newfunction(:stage_from_domain, :type => :rvalue) do |args|
    #e.g. domain_name='osbpr1do'
    domain_name = args[0]
    #we should remove the leading "osb" and the trailing "do"
    if domain_name[0, 3] != 'osb'
     raise ArgumentError, 'domain_name should start with osb' 
    if domain_name[domain_name.length - 2, domain_name.length] != 'do'
     raise ArgumentError, 'domain_name should end with do' 
    domain_name[3, domain_name.length - 5]

The REALLY weirdo thing is how to return the value: simply end your function specifying the rvalue to return (in my case "domain_name[3, domain_name.length - 5]". No old-fashioned, READABLE "return" statements... who needs clarity....

That's all, you can now use the stage_from_domain function inside Puppet. Cool! Maybe after all I will be able to turn Puppet into something manageable... especially the day they will decide to support Groovy, instead of Stinking Ruby.

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