When I run the cluster nodes output and filter out the masters, I see some entries which have slot info and some entries do not have any slot info. For example, has slot info 0-564 slot range and there is no slot info for . What does missing slot-info mean for ? No slots assigned? If no slots are assigned, then the master node is useless?
<MASTER-ID1> <IP-ADDRESS1>:5072@15072 master - 0 1642987445000 206 connected 0-564
<MASTER-ID2> <IP-ADDRESS2>:5073@15073 master - 0 1642987446000 216 connected
Yes, it means there's no slot assigned to the master node. You'd better check if all slots (0 - 16383) have been covered. If not, you should manually assign uncovered slots.
If the master node is not assigned any slots, it can only be used to redirect requests, and it's more or less useless.