This is openshift-sdn, the default network plugin for OpenShift (both OKD and OCP). It uses Open vSwitch to connect pods locally, with VXLAN tunnels to connect different nodes.
OpenShift SDN is designed to be installed by the OpenShift Network Operator, and certain components of it (such as the Deployment and DaemonSet objects) are found there.
This module defines two images: the sdn image, which contains OpenShift SDN (both controller and node components) and the kube-proxy image, which is deployed by the Network Operator for third-party network plugins that need it. (Kube-proxy is built from here rather than from the origin repo so that we only have to maintain kube-proxy bugfix/security backports in one place.)
For historical reasons, OpenShift SDN's types are defined in the
network.openshift.io namespace and are part of the
openshift/api module, despite
being used only when OpenShift SDN is the configured network plugin.
Because the OpenShift aggregated apiserver runs in the pod network,
not on the host network, OpenShift SDN cannot depend on it. Therefore,
although the types are defined in openshift/api, they are actually
implemented as CustomResourceDefinitions in the main apiserver. The
Network Operator creates the CRD definitions.
The network controller is run on the masters to handle cluster-level processing:
- Creating
NetNamespaceobjects corresponding toNamespaces - Creating
HostSubnetobjects corresponding toNodes - Implementing high availability for egress IPs
In older releases, the controller was also responsible for reading the
cluster master configuration and creating the ClusterNetwork object
containing configuration information to be used by the nodes. As of
OpenShift 4.2, the ClusterNetwork is created by the Network
Operator.
The openshift-sdn daemon runs on every node,
reads the ClusterNetwork object and the HostSubnet object for the
node it is running on, and uses that information to configure the node
as part of the cluster. This includes:
-
Providing networking to Pods, as requested by the
openshift-sdnCNI plugin (which is a small shim that just talks to the daemon). -
Setting up the OVS bridge, and managing OVS flows as needed for Pods, Services, NetworkPolicy, and EgressNetworkPolicy; and adding and removing flows as needed for communicating with other nodes.
-
Setting up iptables rules for masquerading outbound traffic, and ensure that OpenShift's own traffic does not get firewalled.
-
Updating OVS flows and iptables rules for static egress IPs.
-
Implementing the Service proxy via a built-in copy of kube-proxy, in either the "userspace" mode, "iptables" mode, or the hybrid "unidling" mode.