my %ssh;
my @hosts = qw/ server1.example.com server2.example.com /;
my @cmd = "list of shell commands ending with reboot";
for my $host (@hosts) {
  $ssh{$host} = Net::OpenSSH->new($host, master_opts => [-i => "/path/to/ssh_key"], async => 1);
  $ssh{$host}->error and die "SSH connection to $host failed: " . $ssh{$host}->error;
}

for my $host (@hosts) {
  $ssh{$host}->system("@cmd");
}