As per my knowledge, you can have multiple master nodes in the same cluster. This is called a multi master cluster. But only one master node will acts as main master or active master. The rest will synch with the master, so that if there is a master node failure, through election (if ex: 3 master nodes you had because typically in a multi node cluster you will have odd number to maintain a quorum) , one is selected and it becomes the primary master node. This is done to main high availability.
As per my knowledge, you can have multiple master nodes in the same cluster. This is called a multi master cluster. But only one master node will acts as main master or active master. The rest will synch with the master, so that if there is a master node failure, through election (if ex: 3 master nodes you had because typically in a multi node cluster you will have odd number to maintain a quorum) , one is selected and it becomes the primary master node. This is done to main high availability.