Keepalived's virtual_router_id - should it be unique per node?
Different VRRP instances should have different virtual_router_id values. Same VRRP instances should have the same value.
You can read the following from man keepalived.conf:
# arbitary unique number 0..255
# used to differentiate multiple instances of vrrpd
# running on the same NIC (and hence same socket).
virtual_router_id 51
To summarize, you need to have the same value on the members of same cluster. If you have another cluster, its members should have another value. The virtual_router_id should be unique per VRRP cluster.