Cluster Host Network

The cluster host network provides the physical network required for Kubernetes management and control, as well as private container networking.

Kubernetes uses logical networks for communication between containers, pods, services, and external sites. These networks are implemented over the cluster host network using the CNI service, Calico, in StarlingX.

All nodes in the cluster must be attached to the cluster host network. This network shares an interface with the management network. A container workload’s external connectivity is either through the OAM port or through other configured ports on both the controller and worker nodes, depending on containerized workload requirements. Container network endpoints will be exposed externally with NodePort Kubernetes services. This exposes selected application containers network ports on all interfaces of both controller nodes and all worker nodes, on either the OAM interface or other configured interfaces for external connectivity on all nodes. This is typically done either directly to the application containers service or through an ingress controller service to reduce external port usage. HA would be achieved through either an external HA load balancer across two or more controller and/or worker nodes, or simply using multiple records (two or more destination controller and/or worker node IPs) for the application’s external DNS entry.

Alternatively, the cluster host network can be deployed as an external network and provides the container workload’s external connectivity as well. Container network endpoints will be exposed externally with NodePort Kubernetes services. This exposes selected Application Containers network ports on all interfaces (e.g. external cluster host interfaces) of both controller nodes and all worker nodes. This would typically be done either directly to the Application Containers service or through an ingress controller service to reduce external port usage. HA would be achieved through either an external HA load balancer across two or more controller and/or worker nodes, or simply using multiple records (2 or more destination controller and/or worker node IPs) for the Application’s external DNS Entry.

If using an external cluster host network, container network endpoints could be exposed through BGP within the Calico CNI service. Calico BGP configuration could be modified to advertise selected Application Container services or the ingress controller service to a BGP Peer, specifying the available next hop controller and/or worker nodes’ cluster host IP Addresses.