device-resource-assignment.md

Device resource assignment

This document describes how Multus builds the list of device IDs for a device resource, and how those IDs are passed to delegate CNI plugins.

Background

A NetworkAttachmentDefinition (NAD) can name a device resource with the k8s.v1.cni.cncf.io/resourceName annotation:

apiVersion: k8s.cni.cncf.io/v1
kind: NetworkAttachmentDefinition
metadata:
  name: sriov-net-a
  annotations:
    k8s.v1.cni.cncf.io/resourceName: intel.com/sriov_net_A
spec:
  config: '{ "cniVersion": "1.0.0", "name": "sriov-net-a", "type": "sriov" }'

Multus does not allocate devices. A device plugin advertises the resource, and kubelet assigns devices per container:

spec:
  containers:
  - name: appcntr1
    resources:
      requests:
        intel.com/sriov_net_A: '2'
  - name: appcntr2
    resources:
      requests:
        intel.com/sriov_net_A: '2'

Kubelet reports that assignment as (pod, container, resource name) -> [device IDs]. Multus reads it from the kubelet pod-resources API, or from the kubelet checkpoint file if that API is unavailable.

For each resource name, Multus concatenates those per-container lists into one pod-wide slice. When a delegate network uses that resource name, Multus takes the next unused ID from the slice and writes it into the delegate CNI configuration as deviceID.

List order

The slice is built as follows:

1. Device IDs allocated to the same container for the same resource name are sorted.
2. Each container's sorted IDs are appended in container order. Devices from different containers are not mixed together.

Example: kubelet allocated 0000:03:02.3 and 0000:03:02.0 to appcntr1, and 0000:03:02.5 and 0000:03:02.1 to appcntr2. The list for intel.com/sriov_net_A is:

["0000:03:02.0", "0000:03:02.3", "0000:03:02.1", "0000:03:02.5"]

Sorting within each container makes the order of device IDs for that container deterministic. Multus does not sort across containers, so kubelet's per-container grouping is unchanged.

Related documentation

• How to use — device plugin and Dynamic Resource Allocation (DRA) examples.
• Configuration — Multus configuration reference.