Doubt with High Availability config

I have doubts with enabling high availability on v6.7. I am trying to upgrade from v6.5 where I had 3 leaf nodes and a master. But while using the steps mentioned here for upgarde: SingleStoreDB Cloud · SingleStore Documentation, it asks to have even number of leaf nodes. Can someone point me to the doc where I can read about the MemSQL’s strategy for having HA?

Thanks