our %services = {
    '1' => {
        name => '...',
        host => { hosta => 1, hostb => 1 },
    }
    '2' => {...}
};

##</code><code>##

my $service = $services{ $user_request };
if ( not $service->{ host }{ $current_host } ) {
    # error here
}
else {
    # real work here
}