The Cluster Network Operator installs and upgrades the networking components on an OpenShift Kubernetes cluster.

It follows the Controller pattern: it reconciles the state of the cluster against a desired configuration. The configuration specified by a CustomResourceDefinition called Network.config.openshift.io/v1, which has a corresponding type.

Most users will be able to use the top-level OpenShift Config API, which has a Network type. The operator will automatically translate the Network.config.openshift.io object in to a Network.operator.openshift.io.

To see the network operator:

$ oc get -o yaml network.operator cluster

When the controller has reconciled and all its dependent resources have converged, the cluster should have an installed network plugin and a working service network. In OpenShift, the Cluster Network Operator runs very early in the install process -- while the boostrap API server is still running.

The network operator gets its configuration from two objects: the Cluster and the Operator configuration. Most users only need to create the Cluster configuration - the operator will generate its configuration automatically. If you need finer-grained configuration of your network, you will need to create both configurations.

Any changes to the Cluster configuration are propagated down in to the Operator configuration. In the event of conflicts, the Operator configuration will be updated to match the Cluster configuration.

For example, if you want to change the service network CIDR, do the following:

Create the cluster using openshift-install and generate the install-config. Use a convenient directory for the cluster.

$ openshift-install --dir=MY_CLUSTER create install-config

Edit the MY_CLUSTER/install-config.yaml and change first value under serviceNetwork to, for example, 10.144.0.0/16.

After that go on with the install.

When you want to change the default networing parameters, for example, you want to use a different MTU, then you will need to create the manifest files.

$ openshift-install --dir=MY_CLUSTER create manifests

The MY_CLUSTER/manifests/cluster-network-02-config.yml contains the cluster network operator configuration. It is the basis of the operator configuration and can't be changed.

The cluster-network-02-config.yml file is copied to a new file and that file is edited for new configuration.

$ cp MY_CLUSTER/manifests/cluster-network-02-config.yml MY_CLUSTER/manifests/cluster-network-03-config.yml

Edit the new file:

• change first line apiVersion: config.openshift.io/v1 to apiVersion: operator.openshift.io/v1

When all configuration changes are complete, go on and create the cluster:

$ openshift-install --dir=MY_CLUSTER create cluster

The following sections detail how to configure the cluster-network-03-config.yml file for different needs.

Cluster config

• Type Name: Network.config.openshift.io
• Instance Name: cluster
• View Command: oc get Network.config.openshift.io cluster -oyaml
• File: install-config.yaml

Operator config

• Type Name: operator.openshift.io/v1
• Instance Name: cluster
• View Command: oc get network.operator cluster -oyaml
• File: manifests/cluster-network-03-config.yml as described above

Cluster Config manifests/cluster-network-02-config.yml

The fields in this file can't be changed. The installer created it from the install.config.yaml file (above).

apiVersion: config.openshift.io/v1
kind: Network
metadata:
  name: cluster
spec:
  clusterNetwork:
  - cidr: 10.128.0.0/14
    hostPrefix: 23
  networkType: OVNKubernetes
  serviceNetwork:
  - 172.30.0.0/16

Corresponding Operator Config manifests/cluster-network-03-config.yml

This config file starts as a copy of manifests/cluster-network-02-config.yml. You can add to the file but you can't change lines in the file.

apiVersion: operator.openshift.io/v1
kind: Network
metadata:
  name: cluster
spec:
  additionalNetworks: null
  clusterNetwork:
  - cidr: 10.128.0.0/14
    hostPrefix: 23
  defaultNetwork:
    type: OVNKubernetes
  serviceNetwork:
  - 172.30.0.0/16

The ClusterNetworks and ServiceNetwork are configured in the MY_CLUSTER/install-config from above. They cannot be changed in the manifests.

Users must supply at least two address pools - ClusterNetwork for pods, and ServiceNetwork for services. Some network plugins, such as OVNKubernetes, support multiple ClusterNetworks. All address blocks must be non-overlapping and a multiple of hostPrefix.

For future expansion, multiple serviceNetwork entries are allowed by the configuration but not actually supported by any network plugins. Supplying multiple addresses is invalid.

Each clusterNetwork entry has an additional parameter, hostPrefix, that specifies the address size to assign to each individual node. For example,

cidr: 10.128.0.0/14
hostPrefix: 23

means 512 nodes would get blocks of size /23, or 512 addresses. If the hostPrefix field is not used by the plugin, it can be left unset.

IP address pools are always read from the Cluster configuration and propagated "downwards" into the Operator configuration. Any changes to the Operator configuration are ignored.

Currently, changing the address pools once set is not supported. In the future, some network providers may support expanding the address pools.

Example:

spec:
  serviceNetwork:
  - "172.30.0.0/16"
  clusterNetwork:
    - cidr: "10.128.0.0/14"
      hostPrefix: 23
    - cidr: "192.168.0.0/18"
      hostPrefix: 23

The default network provider is configured in the MY_CLUSTER/install-config from above. It cannot be changed in the manifests. Different network providers have additional provider-specific settings.

The network type is always read from the Cluster configuration.

Currently, the understood values for networkType are:

• OVNKubernetes

Other values are ignored. If you wish to use use a third-party network provider not managed by the operator, set the network type to something meaningful to you. The operator will not install or upgrade a network provider, but all other Network Operator functionality remains.

OVNKubernetes supports the following configuration options, all of which are optional and once set at cluster creation, they can't be changed except for gatewayConfig and IPsec which can be changed at runtime:

• MTU: The MTU to use for the geneve overlay. The default is the MTU of the node that the cluster-network-operator is first run on, minus 100 bytes for geneve overhead. If the nodes in your cluster don't all have the same MTU then you may need to set this explicitly.
• genevePort: The UDP port to use for the Geneve overlay. The default is 6081.
• hybridOverlayConfig: hybrid linux/windows cluster (see below).
• ipsecConfig: enables and configures IPsec for pods on the pod network within the cluster.
• policyAuditConfig: holds the configuration for network policy audit events.
• gatewayConfig: holds the configuration for node gateway options.
  • routingViaHost: If set to true, pod egress traffic will touch host networking stack before being sent out.
• egressIPConfig: holds the configuration for EgressIP options.
  • reachabilityTotalTimeoutSeconds: Set EgressIP node reachability total timeout in seconds, 0 means disable reachability check and the default is 1 second.

These configuration flags are only in the Operator configuration object.

Example from the manifests/cluster-network-03-config.yml file:

spec:
  defaultNetwork:
    type: OVNKubernetes
    ovnKubernetesConfig:
      mtu: 1400
      genevePort: 6081
      gatewayConfig:
        routingViaHost: false
      egressIPConfig:
        reachabilityTotalTimeoutSeconds: 5

Additionally, you can configure per-node verbosity for ovn-kubernetes. This is useful if you want to debug an issue, and can reproduce it on a single node. To do this, create a special ConfigMap with keys based on the Node's name:

kind: ConfigMap
apiVersion: v1
metadata:
  name: env-overrides
  namespace: openshift-ovn-kubernetes
  annotations:
data:
  # to set the node processes on a single node to verbose
  # replace this with the node's name (from oc get nodes)
  ip-10-0-135-96.us-east-2.compute.internal: |
    OVN_KUBE_LOG_LEVEL=5
    OVN_LOG_LEVEL=dbg
  # to adjust master log levels, use _master
  _master: |
    OVN_KUBE_LOG_LEVEL=5
    OVN_LOG_LEVEL=dbg

OVNKubernetes supports a hybrid cluster of both Linux and Windows nodes on x86_64 hosts. The ovn configuration is done as described above. In addition the hybridOverlayConfig can be included as follows:

Add the following to the spec: section

Example from the manifests/cluster-network-03-config.yml file:

spec:
  defaultNetwork:
    type: OVNKubernetes
    ovnKubernetesConfig:
      hybridOverlayConfig:
        hybridClusterNetwork:
        - cidr: 10.132.0.0/14
          hostPrefix: 23

The hybridClusterNetwork cidr and hostPrefix are used when adding windows nodes. This CIDR must not overlap the ClusterNetwork CIDR or serviceNetwork CIDR.

There can be at most one hybridClusterNetwork "CIDR". A future version may supports multiple cidr.

OVNKubernetes supports IPsec encryption of all pod traffic using the OVN IPsec functionality. Add the following to the spec: section of the operator config:

spec:
  defaultNetwork:
    type: OVNKubernetes
    ovnKubernetesConfig:
      ipsecConfig: {}

OVN Kubernetes supports IPsec encryption dynamic enablement/disablement at runtime. The IPsec protocol adds an ESP header to tenant traffic which stores security data that is needed by each IPsec endpoint to encrypt/decrypt the tenant traffic.

In order for IPsec to function properly the cluster MTU size must be decreased by 46 bytes to fit the additional ESP header added to each packet. This adjustment is not currently automatic and must be performed by the cluster administrator before enabling IPsec at runtime.

Example of enabling the IPsec at runtime:

1. Decrease the Cluster MTU size by 46 bytes (for ESP header):
   1. Add the following to the spec: section of the operator config:

spec:
migration:
  mtu:
    machine:
      from: 1500
      to: 1500
    network:
      from: 1400
      to: 1354

2. wait until Machine-Config-Operator updates the machines, it will reboot each node one by one:

$ oc get mcp

3. finalize the MTU migration process by adding the following to the spec: section of the operator config:

spec:
  migration: null
  defaultNetwork:
    ovnKubernetesConfig:
      ...
      mtu: 1354

For more information about MTU change at runtime

2. Enable IPsec: Add the following to the spec: section of the operator config:

spec:
  defaultNetwork:
    type: OVNKubernetes
    ovnKubernetesConfig:
      ipsecConfig: {}

Example of disabling IPsec at runtime:

$ oc patch networks.operator.openshift.io cluster --type=json -p='[{"op":"remove", "path":"/spec/defaultNetwork/ovnKubernetesConfig/ipsecConfig"}]'

OVNKubernetes supports audit logging of network policy traffic events. Add the following to the spec: section of the operator config:

spec:
  defaultNetwork:
    type: OVNKubernetes
    ovnKubernetesConfig: 
      policyAuditingConfig:
        maxFileSize: 1
        rateLimit: 5
        destination: libc
        syslogFacility: local0

To understand more about each field, and to see the default values check out the Openshift api definition

Some plugins require a standalone kube-proxy to be deployed.

The deployKubeProxy flag can be used to indicate whether CNO should deploy a standalone kube-proxy, but for supported network types, this will default to the correct value automatically.

The configuration here can be used for third-party plugins with a separate kube-proxy process as well.

For plugins that use kube-proxy (whether built-in or standalone), you can configure the proxy via kubeProxyConfig

• iptablesSyncPeriod: The interval between periodic iptables refreshes. Default: 30 seconds. Increasing this can reduce the number of iptables invocations.
• bindAddress: The address to "bind" to - the address for which traffic will be redirected.
• proxyArguments: additional command-line flags to pass to kube-proxy - see the documentation.

The top-level flag deployKubeProxy tells the network operator to explicitly deploy a kube-proxy process. Generally, you will not need to provide this; the operator will decide appropriately.

Example from the manifests/cluster-network-03-config.yml file:

spec:
  deployKubeProxy: false
  kubeProxyConfig:
   iptablesSyncPeriod: 30s
   bindAddress: 0.0.0.0
   proxyArguments:
     iptables-min-sync-period: ["30s"]

Users can configure additional networks, based on Kubernetes Network Plumbing Working Group's Kubernetes Network Custom Resource Definition De-facto Standard Version 1.

• name: name of network attachment definition, required
• namespace: namespace for the network attachment definition. The default is default namespace
• type: specify network attachment definition type, required

Currently, the understood values for type are:

• Raw
• SimpleMacvlan

Example from the manifests/cluster-network-03-config.yml file:

spec:
  additionalNetworks:
  - name: test-network-1
    namespace: namespace-test-1
    type: ...

Then it generates the following network attachment definition:

$ oc -n namespace-test-1 get network-attachment-definitions.k8s.cni.cncf.io
apiVersion: k8s.cni.cncf.io/v1
kind: NetworkAttachmentDefinition
metadata:
  name: test-network-1
  namespace: namespace-test-1
  # (snip)
spec:
  # (snip)

Users can attach the network attachment through Pod annotation, k8s.v1.cni.cncf.io/networks, such as:

apiVersion: v1
kind: Pod
metadata:
  name: test-pod-01
  namespace: namespace-test-1
  annotations:
    k8s.v1.cni.cncf.io/networks: '[
            { "name": "test-network-1" }
    ]'
spec:
  containers:
# (snip)

Please take a look into the spec, Kubernetes Network Plumbing Working Group's Kubernetes Network Custom Resource Definition De-facto Standard Version 1, for its detail.

Users can configure network attachment definition with CNI json as following options required:

• rawCNIConfig: CNI JSON configuration for the network attachment

Example from the manifests/cluster-network-03-config.yml file:

spec:
  additionalNetworks:
  - name: test-network-1
    namespace: namespace-test-1
    rawCNIConfig: '{ "cniVersion": "0.3.1", "type": "macvlan", "master": "eth1", "mode": "bridge", "ipam": { "type": "dhcp" } }'
    type: Raw

This config will generate the following network attachment definition:

apiVersion: k8s.cni.cncf.io/v1
kind: NetworkAttachmentDefinition
metadata:
  # (snip)
  name: test-network-1
  namespace: namespace-test-1
  ownerReferences:
  - apiVersion: operator.openshift.io/v1
    # (snip)
spec:
  config: '{ "cniVersion": "0.3.1", "type": "macvlan", "master": "eth1", "mode": "bridge", "ipam": { "type": "dhcp" } }'

SimpleMacvlan provides user to configure macvlan network attachments. macvlan creates a virtual copy of a master interface and assigns the copy a randomly generated MAC address. The pod can communicate with the network that is attached to the master interface. The distinct MAC address allows the pod to be identified by external network services like DHCP servers, firewalls, routers, etc. macvlan interfaces cannot communicate with the host via the macvlan interface. This is because traffic that is sent by the pod onto the macvlan interface is bypassing the master interface and is sent directly to the interfaces underlying network. Before traffic gets sent to the underlying network it can be evaluated within the macvlan driver, allowing it to communicate with all other pods that created their macvlan interface from the same master interface.

Users can configure macvlan network attachment definition with following parameters, all of which are optional:

• master: master is the host interface to create the macvlan interface from. If not specified, it will be default route interface
• mode: mode is the macvlan mode: bridge, private, vepa, passthru. The default is bridge
• mtu: mtu is the mtu to use for the macvlan interface. if unset, host's kernel will select the value
• ipamConfig: IPAM (IP Address Management) configration: dhcp or static. The default is dhcp

spec:
  additionalNetworks:
  - name: test-network-2
    type: SimpleMacvlan
    simpleMacvlanConfig:
      master: eth0
      mode: bridge
      mtu: 1515
      ipamConfig:
        type: dhcp

Users can configure static IPAM with following parameters:

• addresses:
  • address: Address is the IP address in CIDR format, optional (if no address, assume address will be supplied as pod annotation, k8s.v1.cni.cncf.io/networks)
  • gateway: Gateway is IP inside of subnet to designate as the gateway, optional
• routes: optional
  • destination: Destination points the IP route destination
  • gateway: Gateway is the route's next-hop IP address. If unset, a default gateway is assumed (as determined by the CNI plugin)
• dns: optional
  • nameservers: Nameservers points DNS servers for IP lookup
  • domain: Domain configures the domainname the local domain used for short hostname lookups
  • search: Search configures priority ordered search domains for short hostname lookups

spec:
  additionalNetworks:
  - name: test-network-3
    type: SimpleMacvlan
    simpleMacvlanConfig:
      ipamConfig:
        type: static
        staticIPAMConfig:
          addresses:
          - address: 198.51.100.11/24
            gateway: 198.51.100.10
          routes:
          - destination: 0.0.0.0/0
            gateway: 198.51.100.1
          dns:
            nameservers:
            - 198.51.100.1
            - 198.51.100.2
            domain: testDNS.example
            search:
            - testdomain1.example
            - testdomain2.example

The operator is expected to run as a pod (via a Deployment) inside a kubernetes cluster. It will retrieve the configuration above and reconcile the desired configuration. A suitable manifest for running the operator is located in manifests/.

Most network changes are unsafe to roll out to a production cluster. Therefore, the network operator will stop reconciling if it detects that an unsafe change has been requested.

It is safe to edit the following fields in the Operator configuration:

• deployKubeProxy
• all of kubeProxyConfig

Administrators may wish to forcefully apply a disruptive change to a cluster that is not serving production traffic. To do this, first they should make the desired configuration change to the CRD. Then, delete the network operator's understanding of the state of the system:

oc -n openshift-network-operator delete configmap applied-cluster

Be warned: this is an unsafe operation! It may cause the entire cluster to lose connectivity or even be permanently broken. For example, changing the ServiceNetwork will cause existing services to be unreachable, as their ServiceIP won't be reassigned.