Puppet - test if a package already defined?

Question

I'm writing some puppet modules and have a package defined in two modules hence get the following error:

err: Could not retrieve catalog from remote server: Error 400 on SERVER: Duplicate definition: Package[gnome-session-fallback] is already defined in file /etc/puppet/modules/vnc4server/manifests/init.pp at line 3; cannot redefine at /etc/puppet/modules/vino/manifests/init.pp:7 on node l

Hence want to ensure that the package has not already been defined but the following does not work:

if ! defined ('gnome-session-fallback') {
    package { 'gnome-session-fallback':
        ensure => installed,
    }
}

Can anyone suggest how to fix this, and on the broader scale, what is the "proper" approach to avoiding clashes such as this in modules?

Answer 1

You are missing Package[] inside defined(). The correct way to do it:

if ! defined(Package['gnome-session-fallback']) {
    package { 'gnome-session-fallback':
        ensure => installed,
    }
}

Answer 2

The cleanest way to do this is to use the ensure_resource function from puppetlabs-stdlib:

ensure_resource('package', 'gnome-session-fallback', {'ensure' => 'present'})