Puppet,设置依赖项

我开始设置木偶了.我想设置一个依赖项,在该类尝试安装或启动任何内容之前必须安装邮件传输代理.有了puppet,标准方法似乎设置依赖似乎需要等等.挑战是我不在所有系统上使用相同的MTA.一些系统是实际的邮件服务器我有一个完整的MTA(exim),但我的绝大多数系统都安装了ssmtp.我想要做的是设置一个要求,以便在处理foo类之前安装其中一个MTA并使其正常工作.

这是一个有点展示我想要做的配置.

node default {
  if $fqdn in ["mail1.example.org","mail2.example.org","mail3.example.org"] {

    include fullmta  # mailhub,and so on
  } else {
    include ssmtp    # really basic send-only mta.
  }
  include foo        # class that requries an mta be installed
}

class foo {
  require MTA # FIXME,A valid mta is required.

  package { foo: ensure => present,}
  ... # also a service,and some files,and so on...
}

所以在我的foo类中,我如何要求处理其中一个可能的MTA类？

node default {
  include mta
  include foo        # class that requries an mta be installed
}

class mta {
  if $fqdn in ["mail1.example.org",and so on
  } else {
    include ssmtp    # really basic send-only mta.
  }
}

class foo {
  package { foo: ensure => present,require => Class['mta'],and so on...
}