OpenShift Container Platform supports the Kubernetes Container Network Interface (CNI) as the interface between the OpenShift Container Platform and Kubernetes. Software defined network (SDN) plug-ins match network capabilities to your networking needs. Additional plug-ins that support the CNI interface can be added as needed.

OpenShift SDN

OpenShift SDN is installed and configured by default as part of the Ansible-based installation procedure. See the OpenShift SDN section for more information.

Third-Party SDN plug-ins

Flannel SDN

flannel is a virtual networking layer designed specifically for containers. OpenShift Container Platform can use it for networking containers instead of the default software-defined networking (SDN) components. This is useful if running OpenShift Container Platform within a cloud provider platform that also relies on SDN, such as OpenStack, and you want to avoid encapsulating packets twice through both platforms.


OpenShift Container Platform runs flannel in host-gw mode, which maps routes from container to container. Each host within the network runs an agent called flanneld, which is responsible for:

  • Managing a unique subnet on each host

  • Distributing IP addresses to each container on its host

  • Mapping routes from one container to another, even if on different hosts

Each flanneld agent provides this information to a centralized etcd store so other agents on hosts can route packets to other containers within the flannel network.

The following diagram illustrates the architecture and data flow from one container to another using a flannel network:

Flannel Communication

Node 1 would contain the following routes:

default via dev eth0 proto static metric 100 dev docker0 proto kernel scope link src via dev eth0

Node 2 would contain the following routes:

default via dev eth0 proto static metric 100 dev docker0 proto kernel scope link src via dev eth0

Nuage SDN

Nuage Networks' SDN solution delivers highly scalable, policy-based overlay networking for pods in an OpenShift Container Platform cluster. Nuage SDN can be installed and configured as a part of the Ansible-based installation procedure. See the Advanced Installation section for information on how to install and deploy OpenShift Container Platform with Nuage SDN.

Nuage Networks provides a highly scalable, policy-based SDN platform called Virtualized Services Platform (VSP). Nuage VSP uses an SDN Controller, along with the open source Open vSwitch for the data plane.

Nuage uses overlays to provide policy-based networking between OpenShift Container Platform and other environments consisting of VMs and bare metal servers. The platform’s real-time analytics engine enables visibility and security monitoring for OpenShift Container Platform applications.

Nuage VSP integrates with OpenShift Container Platform to allows business applications to be quickly turned up and updated by removing the network lag faced by DevOps teams.

Nuage VSP Integration with OpenShift Container Platform
Figure 1. Nuage VSP Integration with OpenShift Container Platform

There are two specific components responsible for the integration.

  1. The nuage-openshift-monitor service, which runs as a separate service on the OpenShift Container Platform master node.

  2. The vsp-openshift plug-in, which is invoked by the OpenShift Container Platform runtime on each of the nodes of the cluster.

Nuage Virtual Routing and Switching software (VRS) is based on open source Open vSwitch and is responsible for the datapath forwarding. The VRS runs on each node and gets policy configuration from the controller.

Nuage VSP Terminology

Nuage VSP Building Blocks
Figure 2. Nuage VSP Building Blocks
  1. Domains: An organization contains one or more domains. A domain is a single "Layer 3" space. In standard networking terminology, a domain maps to a VRF instance.

  2. Zones: Zones are defined under a domain. A zone does not map to anything on the network directly, but instead acts as an object with which policies are associated such that all endpoints in the zone adhere to the same set of policies.

  3. Subnets: Subnets are defined under a zone. A subnet is a specific Layer 2 subnet within the domain instance. A subnet is unique and distinct within a domain, that is, subnets within a Domain are not allowed to overlap or to contain other subnets in accordance with the standard IP subnet definitions.

  4. VPorts: A VPort is a new level in the domain hierarchy, intended to provide more granular configuration. In addition to containers and VMs, VPorts are also used to attach Host and Bridge Interfaces, which provide connectivity to Bare Metal servers, Appliances, and Legacy VLANs.

  5. Policy Group: Policy Groups are collections of VPorts.

Mapping of Constructs

Many OpenShift Container Platform concepts have a direct mapping to Nuage VSP constructs:

Nuage VSP and OpenShift Container Platform mapping
Figure 3. Nuage VSP and OpenShift Container Platform mapping

A Nuage subnet is not mapped to an OpenShift Container Platform node, but a subnet for a particular project can span multiple nodes in OpenShift Container Platform.

A pod spawning in OpenShift Container Platform translates to a virtual port being created in VSP. The vsp-openshift plug-in interacts with the VRS and gets a policy for that virtual port from the VSD via the VSC. Policy Groups are supported to group multiple pods together that must have the same set of policies applied to them. Currently, pods can only be assigned to policy groups using the operations workflow where a policy group is created by the administrative user in VSD. The pod being a part of the policy group is specified by means of nuage.io/policy-group label in the specification of the pod.

Integration Components

Nuage VSP integrates with OpenShift Container Platform using two main components:

  1. nuage-openshift-monitor

  2. vsp-openshift plugin


nuage-openshift-monitor is a service that monitors the OpenShift Container Platform API server for creation of projects, services, users, user-groups, etc.

In case of a Highly Available (HA) OpenShift Container Platform cluster with multiple masters, nuage-openshift-monitor process runs on all the masters independently without any change in functionality.

For the developer workflow, nuage-openshift-monitor also auto-creates VSD objects by exercising the VSD REST API to map OpenShift Container Platform constructs to VSP constructs. Each cluster instance maps to a single domain in Nuage VSP. This allows a given enterprise to potentially have multiple cluster installations - one per domain instance for that Enterprise in Nuage. Each OpenShift Container Platform project is mapped to a zone in the domain of the cluster on the Nuage VSP. Whenever nuage-openshift-monitor sees an addition or deletion of the project, it instantiates a zone using the VSDK APIs corresponding to that project and allocates a block of subnet for that zone. Additionally, the nuage-openshift-monitor also creates a network macro group for this project. Likewise, whenever nuage-openshift-monitor sees an addition ordeletion of a service, it creates a network macro corresponding to the service IP and assigns that network macro to the network macro group for that project (user provided network macro group using labels is also supported) to enable communication to that service.

For the developer workflow, all pods that are created within the zone get IPs from that subnet pool. The subnet pool allocation and management is done by nuage-openshift-monitor based on a couple of plug-in specific parameters in the master-config file. However the actual IP address resolution and vport policy resolution is still done by VSD based on the domain/zone that gets instantiated when the project is created. If the initial subnet pool is exhausted, nuage-openshift-monitor carves out an additional subnet from the cluster CIDR to assign to a given project.

For the operations workflow, the users specify Nuage recognized labels on their application or pod specification to resolve the pods into specific user-defined zones and subnets. However, this cannot be used to resolve pods in the zones or subnets created via the developer workflow by nuage-openshift-monitor.

In the operations workflow, the administrator is responsible for pre-creating the VSD constructs to map the pods into a specific zone/subnet as well as allow communication between OpenShift entities (ACL rules, policy groups, network macros, and network macro groups). Detailed description of how to use Nuage labels is provided in the Nuage VSP Openshift Integration Guide.

vsp-openshift Plug-in

The vsp-openshift networking plug-in is called by the OpenShift Container Platform runtime on each OpenShift Container Platform node. It implements the network plug-in init and pod setup, teardown, and status hooks. The vsp-openshift plug-in is also responsible for allocating the IP address for the pods. In particular, it communicates with the VRS (the forwarding engine) and configures the IP information onto the pod.

Kuryr SDN for OpenShift Container Platform

Kuryr (or more specifically Kuryr-Kubernetes) is an SDN solution built using CNI and OpenStack Neutron. Its advantages include being able to use a wide range of Neutron SDN backends and providing interconnectivity between Kubernetes pods and OpenStack virtual machines (VMs).

Kuryr-Kubernetes and OpenShift Container Platform integration is primarily designed for OpenShift Container Platform clusters running on OpenStack VMs.

OpenStack Deployment Requirements

Kuryr SDN has some requirements regarding configuration of OpenStack it will be using. In particular:

  • Minimal service set is Keystone and Neutron.

  • It works with Octavia.

  • Trunk ports extension must be enabled.

  • Neutron must use the Open vSwitch firewall driver.


kuryr-controller is a service responsible for watching OpenShift Container Platform API for new pods being spawned and creating Neutron resources for them. For example, when a pod gets created, kuryr-controller will notice that and call OpenStack Neutron to create a new port. Then, information about that port (or VIF) is saved into the pod’s annotations. kuryr-controller is also able to use precreated port pools for faster pod creation.

Currently, kuryr-controller must be run as a single service instance, so it is modeled in OpenShift Container Platform as Deployment with replicas=1. It requires access to the underlying OpenStack service APIs.


kuryr-cni container serves two roles in Kuryr-Kubernetes deployment. It is responsible for installing and configuring Kuryr CNI script on OpenShift Container Platform nodes and running kuryr-daemon service that is networking the Pods on the host. This means that kuryr-cni container needs to run on every OpenShift Container Platform node, so it is modeled as DaemonSet.

OpenShift Container Platform CNI will call the Kuryr CNI script every time a new pod is spawned on or deleted from an OpenShift Container Platform host. The script fetches the container ID of the local kuryr-cni from Docker API and executes Kuryr CNI plug-in binary through docker exec passing all the CNI call arguments. The plug-in then calls kuryr-daemon over local HTTP socket, again passing all the parameters.

kuryr-daemon service is responsible for watching for Pod’s annotations about Neutron VIFs created for them. When CNI request for given Pod is received daemon either has VIF information in memory already or waits for the annotation to appear on Pod definition. Once VIF info in known all the networking operations happen.