NetworkPolicies for KubeVirt VMs secondary networks using OVN-Kubernetes

Introduction

Kubernetes NetworkPolicies are constructs to control traffic flow at the IP address or port level (OSI layers 3 or 4). They allow the user to specify how a pod (or group of pods) is allowed to communicate with other entities on the network. In simpler words: the user can specify ingress from or egress to other workloads, using L3 / L4 semantics.

Keeping in mind NetworkPolicy is a Kubernetes construct - which only cares about a single network interface - they are only usable for the cluster’s default network interface. This leaves a considerable gap for Virtual Machine users, since they are heavily invested in secondary networks.

The k8snetworkplumbingwg has addressed this limitation by providing a MultiNetworkPolicy CRD - it features the exact same API as NetworkPolicy but can target network-attachment-definitions. OVN-Kubernetes implements this API, and configures access control accordingly for secondary networks in the cluster.

In this post we will see how we can govern access control for VMs using the multi-network policy API. On our simple example, we’ll only allow into our VMs for traffic ingressing from a particular CIDR range.

Current limitations of `MultiNetworkPolicies` for VMs

Kubernetes NetworkPolicy has three types of policy peers:

namespace selectors: allows ingress-from, egress-to based on the peer’s namespace labels
pod selectors: allows ingress-from, egress-to based on the peer’s labels
ip block: allows ingress-from, egress-to based on the peer’s IP address

While MultiNetworkPolicy allows these three types, when used with VMs we recommend using only the IPBlock policy peer - both namespace and pod selectors prevent the live-migration of Virtual Machines (these policy peers require OVN-K managed IPAM, and currently the live-migration feature is only available when IPAM is not enabled on the interfaces).

Demo

To run this demo, we will prepare a Kubernetes cluster with the following components installed:

The following section will show you how to create a KinD cluster, with upstream latest OVN-Kubernetes, upstream latest multus-cni, and the multi-network policy CRDs deployed.

Setup demo environment

Refer to the OVN-Kubernetes repo KIND documentation for more details; the gist of it is you should clone the OVN-Kubernetes repository, and run their kind helper script:

git clone git@github.com:ovn-org/ovn-kubernetes.git

cd ovn-kubernetes
pushd contrib ; ./kind.sh --multi-network-enable ; popd

This will get you a running kind cluster (one control plane, and two worker nodes), configured to use OVN-Kubernetes as the default cluster network, configuring the multi-homing OVN-Kubernetes feature gate, and deploying multus-cni in the cluster.

Install KubeVirt in the cluster

Follow Kubevirt’s user guide to install the latest released version (currently, v1.0.0).

export RELEASE=$(curl https://storage.googleapis.com/kubevirt-prow/release/kubevirt/kubevirt/stable.txt)
kubectl apply -f "https://github.com/kubevirt/kubevirt/releases/download/${RELEASE}/kubevirt-operator.yaml"
kubectl apply -f "https://github.com/kubevirt/kubevirt/releases/download/${RELEASE}/kubevirt-cr.yaml"
kubectl -n kubevirt wait kv kubevirt --timeout=360s --for condition=Available

Now we have a Kubernetes cluster with all the pieces to start the Demo.

Limiting ingress to a KubeVirt VM

In this example, we will configure a MultiNetworkPolicy allowing ingress into our VMs only from a particular CIDR range - let’s say 10.200.0.0/30.

Provision the following NAD (to allow our VMs to live-migrate, we do not define a subnet):

---
apiVersion: k8s.cni.cncf.io/v1
kind: NetworkAttachmentDefinition
metadata:
  name: flatl2net
spec:
  config: |2
    {
            "cniVersion": "0.4.0",
            "name": "flatl2net",
            "type": "ovn-k8s-cni-overlay",
            "topology":"layer2",
            "netAttachDefName": "default/flatl2net"
    }

Let’s now provision our six VMs, with the following name to IP address (statically configured via cloud-init) association:

vm1: 10.200.0.1
vm2: 10.200.0.2
vm3: 10.200.0.3
vm4: 10.200.0.4
vm5: 10.200.0.5
vm6: 10.200.0.6

---
apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
  labels:
    kubevirt.io/vm: vm1
  name: vm1
spec:
  runStrategy: Always
  template:
    metadata:
      labels:
        name: access-control
        kubevirt.io/domain: vm1
        kubevirt.io/vm: vm1
    spec:
      domain:
        devices:
          disks:
          - disk:
              bus: virtio
            name: containerdisk
          - disk:
              bus: virtio
            name: cloudinitdisk
          interfaces:
          - bridge: {}
            name: flatl2-overlay
          rng: {}
        resources:
          requests:
            memory: 1024Mi
      networks:
      - multus:
          networkName: flatl2net
        name: flatl2-overlay
      termination/GracePeriodSeconds: 30
      volumes:
      - containerDisk:
          image: quay.io/kubevirt/fedora-with-test-tooling-container-disk:v1.0.0
        name: containerdisk
      - cloudInitNoCloud:
          networkData: |
            ethernets:
              eth0:
                addresses:
                - 10.200.0.1/24
            version: 2
          userData: |-
            #cloud-config
            user: fedora
            password: password
            chpasswd: { expire: False }
        name: cloudinitdisk
---
apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
  labels:
    kubevirt.io/vm: vm2
  name: vm2
spec:
  runStrategy: Always
  template:
    metadata:
      labels:
        name: access-control
        kubevirt.io/domain: vm2
        kubevirt.io/vm: vm2
    spec:
      domain:
        devices:
          disks:
          - disk:
              bus: virtio
            name: containerdisk
          - disk:
              bus: virtio
            name: cloudinitdisk
          interfaces:
          - bridge: {}
            name: flatl2-overlay
          rng: {}
        resources:
          requests:
            memory: 1024Mi
      networks:
      - multus:
          networkName: flatl2net
        name: flatl2-overlay
      termination/GracePeriodSeconds: 30
      volumes:
      - containerDisk:
          image: quay.io/kubevirt/fedora-with-test-tooling-container-disk:v1.0.0
        name: containerdisk
      - cloudInitNoCloud:
          networkData: |
            ethernets:
              eth0:
                addresses:
                - 10.200.0.2/24
            version: 2
          userData: |-
            #cloud-config
            user: fedora
            password: password
            chpasswd: { expire: False }
        name: cloudinitdisk
---
apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
  labels:
    kubevirt.io/vm: vm3
  name: vm3
spec:
  runStrategy: Always
  template:
    metadata:
      labels:
        name: access-control
        kubevirt.io/domain: vm3
        kubevirt.io/vm: vm3
    spec:
      domain:
        devices:
          disks:
          - disk:
              bus: virtio
            name: containerdisk
          - disk:
              bus: virtio
            name: cloudinitdisk
          interfaces:
          - bridge: {}
            name: flatl2-overlay
          rng: {}
        resources:
          requests:
            memory: 1024Mi
      networks:
      - multus:
          networkName: flatl2net
        name: flatl2-overlay
      termination/GracePeriodSeconds: 30
      volumes:
      - containerDisk:
          image: quay.io/kubevirt/fedora-with-test-tooling-container-disk:v1.0.0
        name: containerdisk
      - cloudInitNoCloud:
          networkData: |
            ethernets:
              eth0:
                addresses:
                - 10.200.0.3/24
            version: 2
          userData: |-
            #cloud-config
            user: fedora
            password: password
            chpasswd: { expire: False }
        name: cloudinitdisk
---
apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
  labels:
    kubevirt.io/vm: vm4
  name: vm4
spec:
  runStrategy: Always
  template:
    metadata:
      labels:
        name: access-control
        kubevirt.io/domain: vm4
        kubevirt.io/vm: vm4
    spec:
      domain:
        devices:
          disks:
          - disk:
              bus: virtio
            name: containerdisk
          - disk:
              bus: virtio
            name: cloudinitdisk
          interfaces:
          - bridge: {}
            name: flatl2-overlay
          rng: {}
        resources:
          requests:
            memory: 1024Mi
      networks:
      - multus:
          networkName: flatl2net
        name: flatl2-overlay
      termination/GracePeriodSeconds: 30
      volumes:
      - containerDisk:
          image: quay.io/kubevirt/fedora-with-test-tooling-container-disk:v1.0.0
        name: containerdisk
      - cloudInitNoCloud:
          networkData: |
            ethernets:
              eth0:
                addresses:
                - 10.200.0.4/24
            version: 2
          userData: |-
            #cloud-config
            user: fedora
            password: password
            chpasswd: { expire: False }
        name: cloudinitdisk
---
apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
  labels:
    kubevirt.io/vm: vm5
  name: vm5
spec:
  runStrategy: Always
  template:
    metadata:
      labels:
        name: access-control
        kubevirt.io/domain: vm5
        kubevirt.io/vm: vm5
    spec:
      domain:
        devices:
          disks:
          - disk:
              bus: virtio
            name: containerdisk
          - disk:
              bus: virtio
            name: cloudinitdisk
          interfaces:
          - bridge: {}
            name: flatl2-overlay
          rng: {}
        resources:
          requests:
            memory: 1024Mi
      networks:
      - multus:
          networkName: flatl2net
        name: flatl2-overlay
      termination/GracePeriodSeconds: 30
      volumes:
      - containerDisk:
          image: quay.io/kubevirt/fedora-with-test-tooling-container-disk:v1.0.0
        name: containerdisk
      - cloudInitNoCloud:
          networkData: |
            ethernets:
              eth0:
                addresses:
                - 10.200.0.5/24
            version: 2
          userData: |-
            #cloud-config
            user: fedora
            password: password
            chpasswd: { expire: False }
        name: cloudinitdisk
---
apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
  labels:
    kubevirt.io/vm: vm6
  name: vm6
spec:
  runStrategy: Always
  template:
    metadata:
      labels:
        name: access-control
        kubevirt.io/domain: vm6
        kubevirt.io/vm: vm6
    spec:
      domain:
        devices:
          disks:
          - disk:
              bus: virtio
            name: containerdisk
          - disk:
              bus: virtio
            name: cloudinitdisk
          interfaces:
          - bridge: {}
            name: flatl2-overlay
          rng: {}
        resources:
          requests:
            memory: 1024Mi
      networks:
      - multus:
          networkName: flatl2net
        name: flatl2-overlay
      termination/GracePeriodSeconds: 30
      volumes:
      - containerDisk:
          image: quay.io/kubevirt/fedora-with-test-tooling-container-disk:v1.0.0
        name: containerdisk
      - cloudInitNoCloud:
          networkData: |
            ethernets:
              eth0:
                addresses:
                - 10.200.0.6/24
            version: 2
          userData: |-
            #cloud-config
            user: fedora
            password: password
            chpasswd: { expire: False }
        name: cloudinitdisk

NOTE: it is important to highlight all the Virtual Machines (and the network-attachment-definition) are defined in the default namespace.

After this step, we should have the following deployment:

Let’s check the VMs vm1 and vm4 can ping their peers in the same subnet. For that we will connect to the VMs over their serial console:

First, let’s check vm1:

➜  virtctl console vm1
Successfully connected to vm1 console. The escape sequence is ^]

[fedora@vm1 ~]$ ping 10.200.0.2 -c 4
PING 10.200.0.2 (10.200.0.2) 56(84) bytes of data.
64 bytes from 10.200.0.2: icmp_seq=1 ttl=64 time=5.16 ms
64 bytes from 10.200.0.2: icmp_seq=2 ttl=64 time=1.41 ms
64 bytes from 10.200.0.2: icmp_seq=3 ttl=64 time=34.2 ms
64 bytes from 10.200.0.2: icmp_seq=4 ttl=64 time=2.56 ms

--- 10.200.0.2 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3005ms
rtt min/avg/max/mdev = 1.406/10.841/34.239/13.577 ms
[fedora@vm1 ~]$ ping 10.200.0.6 -c 4
PING 10.200.0.6 (10.200.0.6) 56(84) bytes of data.
64 bytes from 10.200.0.6: icmp_seq=1 ttl=64 time=3.77 ms
64 bytes from 10.200.0.6: icmp_seq=2 ttl=64 time=1.46 ms
64 bytes from 10.200.0.6: icmp_seq=3 ttl=64 time=5.47 ms
64 bytes from 10.200.0.6: icmp_seq=4 ttl=64 time=1.74 ms

--- 10.200.0.6 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3007ms
rtt min/avg/max/mdev = 1.459/3.109/5.469/1.627 ms
[fedora@vm1 ~]$ 

And from vm4:

➜  ~ virtctl console vm4
Successfully connected to vm4 console. The escape sequence is ^]

[fedora@vm4 ~]$ ping 10.200.0.1 -c 4
PING 10.200.0.1 (10.200.0.1) 56(84) bytes of data.
64 bytes from 10.200.0.1: icmp_seq=1 ttl=64 time=3.20 ms
64 bytes from 10.200.0.1: icmp_seq=2 ttl=64 time=1.62 ms
64 bytes from 10.200.0.1: icmp_seq=3 ttl=64 time=1.44 ms
64 bytes from 10.200.0.1: icmp_seq=4 ttl=64 time=0.951 ms

--- 10.200.0.1 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3006ms
rtt min/avg/max/mdev = 0.951/1.803/3.201/0.843 ms
[fedora@vm4 ~]$ ping 10.200.0.6 -c 4
PING 10.200.0.6 (10.200.0.6) 56(84) bytes of data.
64 bytes from 10.200.0.6: icmp_seq=1 ttl=64 time=1.85 ms
64 bytes from 10.200.0.6: icmp_seq=2 ttl=64 time=1.02 ms
64 bytes from 10.200.0.6: icmp_seq=3 ttl=64 time=1.27 ms
64 bytes from 10.200.0.6: icmp_seq=4 ttl=64 time=0.970 ms

--- 10.200.0.6 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3005ms
rtt min/avg/max/mdev = 0.970/1.275/1.850/0.350 ms

We will now provision a MultiNetworkPolicy applying to all the VMs defined above. To do this mapping correcly, the policy has to:

Be in the same namespace as the VM.
Set k8s.v1.cni.cncf.io/policy-for annotation matching the secondary network used by the VM.
Set matchLabels selector matching the labels set on VM’s spec.template.metadata.

This policy will allow ingress into these access-control labeled pods only if the traffic originates from within the 10.200.0.0/30 CIDR range (IPs 10.200.0.1-3).

---
apiVersion: k8s.cni.cncf.io/v1beta1
kind: MultiNetworkPolicy
metadata:
  name:  ingress-ipblock
  annotations:
    k8s.v1.cni.cncf.io/policy-for: default/flatl2net
spec:
  podSelector:
    matchLabels:
        name: access-control
  policyTypes:
  - Ingress
  ingress:
  - from:
    - ipBlock:
        cidr: 10.200.0.0/30

Taking into account our example, only vm1, vm2, and vm3 will be able to contact any of its peers, as pictured by the following diagram:

MultiNetworkPolicy is provisioned

Let’s try again the ping after provisioning the MultiNetworkPolicy object:

From vm1 (inside the allowed ip block range):

[fedora@vm1 ~]$ ping 10.200.0.2 -c 4
PING 10.200.0.2 (10.200.0.2) 56(84) bytes of data.
64 bytes from 10.200.0.2: icmp_seq=1 ttl=64 time=6.48 ms
64 bytes from 10.200.0.2: icmp_seq=2 ttl=64 time=4.40 ms
64 bytes from 10.200.0.2: icmp_seq=3 ttl=64 time=1.28 ms
64 bytes from 10.200.0.2: icmp_seq=4 ttl=64 time=1.51 ms

--- 10.200.0.2 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3006ms
rtt min/avg/max/mdev = 1.283/3.418/6.483/2.154 ms
[fedora@vm1 ~]$ ping 10.200.0.6 -c 4
PING 10.200.0.6 (10.200.0.6) 56(84) bytes of data.
64 bytes from 10.200.0.6: icmp_seq=1 ttl=64 time=3.81 ms
64 bytes from 10.200.0.6: icmp_seq=2 ttl=64 time=2.67 ms
64 bytes from 10.200.0.6: icmp_seq=3 ttl=64 time=1.68 ms
64 bytes from 10.200.0.6: icmp_seq=4 ttl=64 time=1.63 ms

--- 10.200.0.6 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3006ms
rtt min/avg/max/mdev = 1.630/2.446/3.808/0.888 ms

From vm4 (outside the allowed ip block range):

[fedora@vm4 ~]$ ping 10.200.0.1 -c 4
PING 10.200.0.1 (10.200.0.1) 56(84) bytes of data.

--- 10.200.0.1 ping statistics ---
4 packets transmitted, 0 received, 100% packet loss, time 3083ms

[fedora@vm4 ~]$ ping 10.200.0.6 -c 4
PING 10.200.0.6 (10.200.0.6) 56(84) bytes of data.

--- 10.200.0.6 ping statistics ---
4 packets transmitted, 0 received, 100% packet loss, time 3089ms

Conclusions

In this post we’ve shown how MultiNetworkPolicies can be used to provide access control to VMs with secondary network interfaces.

We have provided a comprehensive example on how a policy can be used to limit ingress to our VMs only from desired sources, based on the client’s IP address.