Node-specific configuration (multiple definition matching)

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I have been fighting with puppet for days and haven't yet figured out how to achieve what I want:

node /a[0-9]*/ {
  class { 'apache':
    default_mods => true,
    mpm_module   => 'itk',
    keepalive    => Off,
    timeout      => 60
  }
  package { 'php5': }
  apache::mod { 'rewrite': }
  apache::mod { 'php5': }
}

This part works fine. Apache gets installed on anything I turn on starting with 'a'. Now I need to create node-specific virtualhost definitions, a la

node a1 {
  file { '/var/www/michael.com}':
    ensure => 'directory',
  }
  file { '/var/www/michael.com/public':
    ensure => 'directory',
  }
  file { '/var/www/michael.com/log':
    ensure => 'directory',
  }
  apache::vhost { 'michael.com':
    docroot => '/var/www/michael.com ...