In this case the solution (cross-coverage) worked for that organization. However I agree that more often than not, it won't work. I didn't have the word-count

In this case the solution (cross-coverage) worked for that organization. However I agree that more often than not, it won't work. I didn't have the word-count to go into this (that could be the topic of an entire book... or at least a chapter of The Practice of Cloud System Administration [https://the-cloud-book.com/ https://the-cloud-book.com/]). That said, my personal rule of thumb is: 6 is the minimum for an oncall roster; 5 if there is another team doing follow-the-sun coverage. YMMV of course. Tom