my @keys = keys %{$nodemetrics{'server1'}};

##</code><code>##

$ perl scratch.pl 
[...]
          'server1' => {
                         'memory' => '1024',
                         'network' => '2200',
                         'cpu' => '30',
                         'disk' => '100'
                       },
[...]

$ perl scratch.pl
[...]
          'server1' => {
                         'disk' => '1024',
                         'memory' => '2200',
                         'cpu' => '30',
                         'network' => '100'
                       }
[...]


##</code><code>##

my @system_attributes = qw(memory cpu disk network);

[...]

my $hashref = $nodemetrics{'server1'};
@$hashref{@system_attributes}=@data;