Duplicate declaration of same resource defined in separate classes

Question

I have a class definition which requires the build-essential package:

class erlang($version = '17.3') {

  package { "build-essential": 
    ensure => installed
  }
  ...
}

Another class in a different module also requires the build-essential package:

class icu {

  package { "build-essential": 
    ensure => installed
  }
  ...
}

However, when I try to perform puppet apply, the error I receive is:

Error: Duplicate declaration: Package[build-essential] is already declared in file /vagrant/modules/erlang/manifests/init.pp:18; cannot redeclare at /vagrant/modules/libicu/manifests/init.pp:17 on node vagrant-ubuntu-trusty-64.home

I was expecting classes to encapsulate the resources they use but this doesn't seem to be the case? How can I resolve this clash?

Answer 1

This is common question when dealing with multiple modules.

There's a number of ways of doing this, the best practise is to modularise and allow the installation of build essential as a parameter:

class icu ($manage_buildessential = false){

  if ($manage_buildessential == true) {
   package { "build-essential": 
     ensure => installed
   }
 }
}

Then, where you want to include your ICU class:

class {'icu':
   manage_buildessential => 'false',
}

However, for a quick and dirty fix:

if ! defined(Package['build-essential']) {
    package { 'build-essential': ensure => installed }
}

Or if you have puppetlabs-stdlib module:

ensure_packages('build-essential')