I am getting this error" 

Failed to load cache value. :: {"error":"config service URL is not set in settings", "authority":"AsService", "configSet":"services/qscheduler-swarming-dev", "path":"config.cfg"}

when spinning up a new appengine app. The error description doesn't do much to point me in a useful direction (e.g. which settings do I need to be editing to point a which config service?); and it took me a fair bit of grepping to trace this to luci/config/appengine/gaeconfig/default.go (and I'm still trying to reverse engineer what I need to do from there).