./apache/manifests/init.pp
class apache(
 String $package_name,
) {
 class { 'apache::install': }
 -> class { 'apache::config': }
 ~> class { 'apache::service': }
 contain apache::install
 contain apache::config
 contain apache::service
}

./apache/manifests/install.pp
class apache::install {
 $package_name = $apache::package_name

 if $facts['osfamily'] == 'redhat' {
 package { 'mod_ssl':
 ensure => installed,
 }
 }

 package { $package_name:
 ensure => installed,
 }
}