Both approaches have merits and demerits of course, and could be combined too. BTW, for GB/UK sites my own system publishes flags easily testable over HTTP (se

Both approaches have merits and demerits of course, and could be combined too. BTW, for GB/UK sites my own system publishes flags easily testable over HTTP (see foot of https://www.earth.org.uk/_gridCarbonIntensityGB.html https://www.earth.org.uk/_gridCarbonIntensityGB.html page) and I used to test those on my cloud UK services when I had them, but I also used to defer non-essential work in servers all over the world at their local peak grid times of day.