The Route Agent component runs on every node in each participating cluster. It is responsible for setting up the necessary host network elements on top of the existing Kubernetes CNI plugin.
The Route Agent receives the detected CNI plugin as part of its configuration.
For CNI plugins that utilize kube-proxy in iptables mode, the Route Agent is responsible for setting up VXLAN tunnels and routing the cross cluster traffic from the node to the cluster’s active Gateway Engine which subsequently sends the traffic to the destination cluster.
When running on the same node as the active Gateway Engine, Route Agent creates a VXLAN VTEP interface to which Route Agent instances running on the other worker nodes in the local cluster connect by establishing a VXLAN tunnel with the VTEP of the active Gateway Engine node. The MTU of the VXLAN tunnel is configured based on the MTU of the default interface on the host minus the VXLAN overhead.
Route Agents use Endpoint resources synced from other clusters to configure
routes and to program the necessary iptables rules to enable full cross-cluster
connectivity.
When the active Gateway Engine fails and a new Gateway Engine takes over, Route Agents will automatically update the route tables on each node to point to the new active Gateway Engine node.
For the OVN Kubernetes CNI plugin, host network routing is configured on all nodes and,
on the active Gateway node, IP forwarding is configured between the ovn-k8s-gw0
and cable interfaces.