output

[root@localhost ~]# puppet apply test.pp
Notice: Scope(Backends[volume]): ceph2 lvm1 ceph1
Notice: Compiled catalog for localhost.localdomain.domain.name in environment production in 0.03 seconds
Notice: Finished catalog run in 0.05 seconds

test.pp

Backends<| title == 'volume' |> {
  backends +> 'ceph2'
}

Backends<| title == 'volume' |> {
  backends +> 'lvm1'
}

Backends<| title == 'volume' |> {
  backends +> 'ceph1'
}

backends {'volume':}

define backends(
  $backends = []
){
  notice($backends)
}