[ishandotpage]

I agree with you that this question is unanswerable verbatim. It sorta reminds me of how Agile came up the "Definition of Done"

System maintainers / stakeholders themselves need to come up with a "Definition of Working"

Since distributed systems are basically in some state of failure/degradation almost all of the time, it is useless to try to say that "the system is working when there are no errors anywhere".

Some sort of threshold needs to be arrived at where we can say "it's working".

What that threshold looks like is going to vary from project to project.