An external load balancer is provided by you. The specifics on which load balancer to use and the exact configuration are beyond the scope of this documentation.
The load balancer should be configured:
to direct traffic to all available nodes
with the cluster certificate
to use /ping as the health endpoint for eah node in your cluster
The load balancer does not need to be configured for session affinity/stickiness. Session affinity is automatically handled inside the cluster.
Requests to any node in the cluster will be automatically load balanced by the system to nodes across the cluster. This provides a basic level of load balancing regardless of the presence of an external load balancer. An alternative is to use DNS round robin load balancing, in which the cluster DNS hostname resolves to each node in the cluster.