Add prometheus node-exporter name for Ubuntu

[ilhaan]

Pull Request (PR) description

Add package prometheus-node-exporter package name for Debian.

This Pull Request (PR) fixes the following issues

Installation on Ubuntu 18.04

[anarcat]

PR #303 used to do this. because this change breaks other expectations (it's why tests fail here), I pulled it out to make it easier to merge debian support.

instead of patching the module here, I call the profile with this:

# our node exporter configuration
#
# @param ensure if this node_exporter should be added or removed
class profile::prometheus::node_exporter(
  Enum['present', 'absent'] $ensure = 'present',
) {
  $package_ensure = $ensure ? { 'present' => 'installed', 'absent' => 'absent' }
  $service_ensure = $ensure ? { 'present' => 'running', 'absent'  => 'stopped' }
  class { 'prometheus::node_exporter':
    package_ensure    => $package_ensure,
    service_ensure    => $service_ensure,
    export_scrape_job => true,
    scrape_job_labels => {
      'alias'   => $facts['fqdn'],
      'classes' => join(lookup('classes', Data, 'first', []), ',')
    },
    # force debian package install parameters, further discussion in:
    # https://github.com/voxpupuli/puppet-prometheus/pull/303
    install_method    => 'package',
    init_style        => 'none',
    user              => 'prometheus',
    group             => 'prometheus',
    package_name      => 'prometheus-node-exporter',
    service_name      => 'prometheus-node-exporter',
    # purge_config_dir => true,
  }

  # XXX: should be using apt::pin, but that involves replacing a lot
  # of our custom code
  file {
    '/etc/apt/preferences.d/prometheus-node-exporter.pref':
      ensure  => (versioncmp($::lsbmajdistrelease, '9') <= 0) ? {
        true  => 'present',
        false => 'absent',
      },
      content => "# this file is managed through puppet, local changes will be lost
Explanation: Prometheus 2.x is not in Debian stretch, remove when we move to buster
Package: prometheus-node-exporter
Pin: release n=stretch-backports
Pin-Priority: 500
",
      notify  => Package['prometheus-node-exporter'],
  }
}

.. but I would love to see this fixed in the upstream code as well. note that you also need to fix the package_name if you want to install from packages, and you will also need to perform this change across other exporters as well...

so it is not as simple as it first looks. :)

good luck!