Configuring PXE booting for virtual machines - Virtual machines | Virtualization

Prerequisites
PXE booting with a specified MAC address
OpenShift Virtualization networking glossary

PXE booting, or network booting, is available in OpenShift Virtualization. Network booting allows a computer to boot and load an operating system or other program without requiring a locally attached storage device. For example, you can use it to choose your desired OS image from a PXE server when deploying a new host.

Prerequisites

A Linux bridge must be connected.
The PXE server must be connected to the same VLAN as the bridge.

PXE booting with a specified MAC address

As an administrator, you can boot a client over the network by first creating a NetworkAttachmentDefinition object for your PXE network. Then, reference the network attachment definition in your virtual machine instance configuration file before you start the virtual machine instance. You can also specify a MAC address in the virtual machine instance configuration file, if required by the PXE server.

Prerequisites

A Linux bridge must be connected.
The PXE server must be connected to the same VLAN as the bridge.

Procedure

Configure a PXE network on the cluster:

Create the network attachment definition file for PXE network pxe-net-conf:

apiVersion: "k8s.cni.cncf.io/v1"
kind: NetworkAttachmentDefinition
metadata:
  name: pxe-net-conf (1)
spec:
  config: |
    {
      "cniVersion": "0.3.1",
      "name": "pxe-net-conf", (2)
      "type": "bridge", (3)
      "bridge": "bridge-interface", (4)
      "macspoofchk": false, (5)
      "vlan": 100, (6)
      "preserveDefaultVlan": false (7)
    }

1	The name for the `NetworkAttachmentDefinition` object.
2	The name for the configuration. It is recommended to match the configuration name to the `name` value of the network attachment definition.
3	The actual name of the Container Network Interface (CNI) plugin that provides the network for this network attachment definition. This example uses a Linux bridge CNI plugin. You can also use an OVN-Kubernetes localnet or an SR-IOV CNI plugin.
4	The name of the Linux bridge configured on the node.
5	Optional: A flag to enable the MAC spoof check. When set to `true`, you cannot change the MAC address of the pod or guest interface. This attribute allows only a single MAC address to exit the pod, which provides security against a MAC spoofing attack.
6	Optional: The VLAN tag. No additional VLAN configuration is required on the node network configuration policy.
7	Optional: Indicates whether the VM connects to the bridge through the default VLAN. The default value is `true`.

Create the network attachment definition by using the file you created in the previous step:
```
$ oc create -f pxe-net-conf.yaml
```
Edit the virtual machine instance configuration file to include the details of the interface and network.
1. Specify the network and MAC address, if required by the PXE server. If the MAC address is not specified, a value is assigned automatically.
  
  Ensure that bootOrder is set to 1 so that the interface boots first. In this example, the interface is connected to a network called <pxe-net>:
  interfaces: - masquerade: {} name: default - bridge: {} name: pxe-net macAddress: de:00:00:00:00:de bootOrder: 1
  Boot order is global for interfaces and disks.
2. Assign a boot device number to the disk to ensure proper booting after operating system provisioning.
  
  Set the disk bootOrder value to 2:
  devices: disks: - disk: bus: virtio name: containerdisk bootOrder: 2
3. Specify that the network is connected to the previously created network attachment definition. In this scenario, <pxe-net> is connected to the network attachment definition called <pxe-net-conf>:
  networks: - name: default pod: {} - name: pxe-net multus: networkName: pxe-net-conf

Create the virtual machine instance:

$ oc create -f vmi-pxe-boot.yaml

Example output

  virtualmachineinstance.kubevirt.io "vmi-pxe-boot" created

Wait for the virtual machine instance to run:

$ oc get vmi vmi-pxe-boot -o yaml | grep -i phase
  phase: Running

View the virtual machine instance using VNC:
```
$ virtctl vnc vmi-pxe-boot
```
Watch the boot screen to verify that the PXE boot is successful.
Log in to the virtual machine instance:
```
$ virtctl console vmi-pxe-boot
```

Verification

Verify the interfaces and MAC address on the virtual machine and that the interface connected to the bridge has the specified MAC address. In this case, we used eth1 for the PXE boot, without an IP address. The other interface, eth0, got an IP address from OpenShift Container Platform.
```
$ ip addr
```
Example output
```
...
3. eth1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
   link/ether de:00:00:00:00:de brd ff:ff:ff:ff:ff:ff
```

OpenShift Virtualization networking glossary

The following terms are used throughout OpenShift Virtualization documentation:

Container Network Interface (CNI): A Cloud Native Computing Foundation project, focused on container network connectivity. OpenShift Virtualization uses CNI plugins to build upon the basic Kubernetes networking functionality.
Multus: A "meta" CNI plugin that allows multiple CNIs to exist so that a pod or virtual machine can use the interfaces it needs.
Custom resource definition (CRD): A Kubernetes API resource that allows you to define custom resources, or an object defined by using the CRD API resource.
Network attachment definition (NAD): A CRD introduced by the Multus project that allows you to attach pods, virtual machines, and virtual machine instances to one or more networks.
Node network configuration policy (NNCP): A CRD introduced by the nmstate project, describing the requested network configuration on nodes. You update the node network configuration, including adding and removing interfaces, by applying a NodeNetworkConfigurationPolicy manifest to the cluster.