sub factory
{
    return $instance if defined $instance;

    my $sName = $main::imscpConfig{'NAMED_SERVER'};

    if (defined $main::execmode && $main::execmode eq 'setup') {
        if ($sName eq 'external_server'
            && $main::imscpOldConfig{'NAMED_SERVER'} ne ''
            && $main::imscpOldConfig{'NAMED_SERVER'} ne $sName
        ) {
            my $package = "Servers::named::$main::imscpOldConfig{'NAMED_SERVER'}";
            eval "require $package";
            fatal( $@ ) if $@;

            my $rs = $package->getInstance()->uninstall();
            fatal( sprintf( "Could not uninstall `%s' server", $main::imscpOldConfig{'NAMED_SERVER'} ) ) if $rs;
        }
    }

    my $package = ($sName eq 'external_server') ? 'Servers::noserver' : "Servers::named::$sName";
    eval "require $package";
    fatal( $@ ) if $@;
    $instance = $package->getInstance();
}