A protocol for backends to communicate load to balancers in real time has appeal. You could hack it in HTTP or similar with X-Server-Load: 0.1234 Perhaps a series of numbers representing different moving averages, etc.
As to what that represents, that must surely depend on the bottlenecks in a particular system. A backend doing heavy number-crunching and one doing lots of complex SQL queries have different loads, and a good load measure for one may be meaningless if applied to the other. How would a 'universal' measure reflect that kind of difference? Where I think you could usefully focus is on standardising a protocol for backends to communicate loads to balancers. That then becomes something we can implement in an lb method module in HTTPD. But it has to be left to individual backend systems exactly how they measure their own loads. -- Nick Kew
