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xcluster-cni

Xcluster-cni is a CNI-plugin for Kubernetes. It is developed for xcluster but can be used in any K8s cluster. Key features;

  • Multi networking - xcluster-cni can create POD-POD connectivity on secondary networks. Multus can be used to bring in extra interfaces to PODs

  • Flexible - Making it useful for experiments. But it also lay a greater responsibility on the user. For instance network overlays are not directly supported, but you can create them yourself

  • Very small footprint - xcluster-cni setup routes and watches the K8s node objects. If the K8s node objects doesn't change often the overhead created by xcluster-cni is basically none

The main components of xcluster-cni are:

  • kube-node IPAM. Reads information (address ranges) from the K8s node object and assigns addresses by delegating to the host-local ipam

  • The xcluster-cni router binary. Sets up routing to address ranges (CIDRs) between K8s nodes. This is deployed as a DaemonSet that will also install (and upgrade) the CNI-plugin on the nodes.

To install xcluster-cni as the main K8s CNI-plugin make sure --allocate-node-cidrs=true is given to the kube-controller-manager and do:

kubectl apply -n kube-system -f https://raw.githubusercontent.com/Nordix/xcluster-cni/master/xcluster-cni.yaml

Multi Networking

A key feature is multi networking. Xcluster-cni can be installed on different interfaces on K8s nodes and can create POD-POD connectivity on secondary networks using Multus. Installing xcluster-cni on secondary networks requires annotations on Node objects:

kubectl annotate node vm-003 cidr.example.com/net3=192.168.55.0/26,fd00:5::1:0/112
kubectl annotate node vm-003 adr.example.com/net3=192.168.2.3,1000::1:c0a8:203

and configuring the annotation names as environment variables:

        env:
          - name: NODE_NAME
            valueFrom:
              fieldRef:
                fieldPath: spec.nodeName
          - name: LOG_LEVEL
            value: "debug"
          - name: CIDR_ANNOTATION
            value: "cidr.example.com/net3"
          - name: ADDRESS_ANNOTATION
            value: "adr.example.com/net3"
          - name: PROTOCOL
            value: "200"

The protocol is used to handle routes and must be unique for each xcluster-cni instance on the node. Default is 202.

Network overlay

xcluster-cni does not setup a network overlay, but you may configure an overlay yourself (e.g. vxlan) and use the ADDRESS_ANNOTATION environment variable to stear traffic to the overlay.

This area will see some improvements in the future.

Network policies

K8s network policies are not supported.

MTU

If xcluster-cni is installed as main K8s CNI-plugin MTU is handled. You may check with:

# cat /etc/cni/net.d/10-xcluster-cni.conf 
{
    "cniVersion": "0.4.0",
    "name": "xcluster",
    "type": "bridge",
    "bridge": "cbr0",
    "isGateway": true,
    "mtu": 9000,
    "hairpinMode": true,
    "isDefaultGateway": true,
    "ipam": {
        "type": "kube-node",
        "kubeconfig": "/etc/cni/net.d/xcluster-cni.kubeconfig",
        "dataDir": "/run/container-ipam-state/xcluster"
    }
}

In this example "jumbo-frames" with mtu=9000 are used.

For secondary networks the MTU must be set in the Multus NAD object and is the users responsibility.

Build the xcluster-cni image

The image is built with "docker build" so docker must be installed.

./build.sh         # Help printout
./build.sh image   # Build the image