Surely you'd have some sort of remote KVM in such cases (like IPMI, as mentioned in another comment). That's critical in the clusters I've run and, of course,

Surely you'd have some sort of remote KVM in such cases (like IPMI, as mentioned in another comment). That's critical in the clusters I've run and, of course, the manufacturers' implementation of that critical functionality in IPMI is likely to be rubbish and you can't get it fixed...