Final answer:
Nodes can join a cluster in customer-hosted runtime planes either by manual configuration or automated discovery, with manual requiring specific setup steps by an administrator and automated allowing for self-configuration using discovery protocols.
Step-by-step explanation:
The two ways how nodes (runtimes) can join a cluster in customer-hosted runtime plane are through manual configuration and through automated discovery. In the manual configuration approach, an administrator would provide configuration details to each node to join the cluster. This process usually involves setting up network details, cluster identifiers, and node-specific parameters. On the other hand, automated discovery relies on protocols and services designed to help the nodes discover each other and self-configure to form a cluster. This often uses multicast networking, service registries or other discovery mechanisms.