Assuming you decide to do a mesh cluster. (Meaning all 3 nodes will cluster using default port 3002 over TCP)
You can do the following.
Get IP address for all 3 nodes:
(Run ip addr or similar command on each node and capture the 3 ip addresses from interface you want to use for heartbeats)
Node1 IP: w.x.y.1
Node2 IP: w.x.y.2
Node3 IP: w.x.y.3
Modify the config under each node by editing /etc/aerospike/aerospike.conf and adding mesh-seed-address-port IPs to the heartbeat section:
mode mesh # Send heartbeats using Mesh (Unicast) protocol
# address eth1 # (Optional) (Default: any) IP of the NIC on
# which this node is listening to heartbeat
port 3002 # port on which this node is listening to
# IP addresses for seed nodes in the cluster
mesh-seed-address-port w.x.y.1 3002 # IP address for seed node in the cluster
mesh-seed-address-port w.x.y.2 3002 # IP address for seed node in the cluster
mesh-seed-address-port w.x.y.3 3002 # IP address for seed node in the cluster
interval 150 # Number of milliseconds between heartbeats
timeout 10 # Number of heartbeat intervals to wait before
# timing out a node
and finally restart the 3 servers.
sudo service aerospike restart
You should be able to use a tool like asadm to check the health of your cluster.
asadm -e info
Please also architecture info on clustering: