re: how do you even begin to debug that when something goes wrong
you start at the function that errored and work your way back through the logs.
Having an http log of every function call actually makes this easier than debugging functions calling functions in a monolithic app. They don't all emit logs.
New stuff is hard but so was the old stuff. You spent time learning the old stuff. Maybe it's time to specialise if keeping up is becoming tiresome.
Biting the hand that feeds IT
