It is not always practical to create checks for all possible errors. E. g. broken node can return 404 for URL-X and 200 for all other used URLs. And this URL-X

It is not always practical to create checks for all possible errors. E. g. broken node can return 404 for URL-X and 200 for all other used URLs. And this URL-X can be "hot" at that time. I think it is not bad to monitor response time for backends and flag some alert if one node has response time significantly lower than mean among all nodes (with comparable hardware).