node-feature-discovery/docs/get-started/introduction.md

---
title: "Introduction"
layout: default
sort: 1
---

# Introduction
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## Table of contents
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1. TOC
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---

This software enables node feature discovery for Kubernetes. It detects
hardware features available on each node in a Kubernetes cluster, and
advertises those features using node labels.

NFD consists of three software components:

1. nfd-master
1. nfd-worker
1. nfd-topology-updater

## NFD-Master

NFD-Master is the daemon responsible for communication towards the Kubernetes
API. That is, it receives labeling requests from the worker and modifies node
objects accordingly.

## NFD-Worker

NFD-Worker is a daemon responsible for feature detection. It then communicates
the information to nfd-master which does the actual node labeling.  One
instance of nfd-worker is supposed to be running on each node of the cluster,

## NFD-Topology-Updater

NFD-Topology-Updater is a daemon responsible for examining allocated
resources on a worker node to account for resources available to be allocated
to new pod on a per-zone basis (where a zone can be a NUMA node). It then
communicates the information to nfd-master which does the
[NodeResourceTopology CR](#noderesourcetopology-cr) creation corresponding
to all the nodes in the cluster. One instance of nfd-topology-updater is
supposed to be running on each node of the cluster.

## Feature Discovery

Feature discovery is divided into domain-specific feature sources:

- CPU
- IOMMU
- Kernel
- Memory
- Network
- PCI
- Storage
- System
- USB
- Custom (rule-based custom features)
- Local (hooks for user-specific features)

Each feature source is responsible for detecting a set of features which. in
turn, are turned into node feature labels.  Feature labels are prefixed with
`feature.node.kubernetes.io/` and also contain the name of the feature source.
Non-standard user-specific feature labels can be created with the local and
custom feature sources.

An overview of the default feature labels:

```json
{
  "feature.node.kubernetes.io/cpu-<feature-name>": "true",
  "feature.node.kubernetes.io/custom-<feature-name>": "true",
  "feature.node.kubernetes.io/iommu-<feature-name>": "true",
  "feature.node.kubernetes.io/kernel-<feature name>": "<feature value>",
  "feature.node.kubernetes.io/memory-<feature-name>": "true",
  "feature.node.kubernetes.io/network-<feature-name>": "true",
  "feature.node.kubernetes.io/pci-<device label>.present": "true",
  "feature.node.kubernetes.io/storage-<feature-name>": "true",
  "feature.node.kubernetes.io/system-<feature name>": "<feature value>",
  "feature.node.kubernetes.io/usb-<device label>.present": "<feature value>",
  "feature.node.kubernetes.io/<file name>-<feature name>": "<feature value>"
}
```

## Node annotations

NFD also annotates nodes it is running on:

| Annotation                                                   | Description
| ------------------------------------------------------------ | -----------
| [&lt;instance&gt;.]nfd.node.kubernetes.io/master.version     | Version of the nfd-master instance running on the node. Informative use only.
| [&lt;instance&gt;.]nfd.node.kubernetes.io/worker.version     | Version of the nfd-worker instance running on the node. Informative use only.
| [&lt;instance&gt;.]nfd.node.kubernetes.io/feature-labels     | Comma-separated list of node labels managed by NFD. NFD uses this internally so must not be edited by users.
| [&lt;instance&gt;.]nfd.node.kubernetes.io/extended-resources | Comma-separated list of node extended resources managed by NFD. NFD uses this internally so must not be edited by users.

NOTE: the [`--instance`](../advanced/master-commandline-reference.md#instance)
command line flag affects the annotation names

Unapplicable annotations are not created, i.e. for example master.version is
only created on nodes running nfd-master.

## NodeResourceTopology CR

When run with NFD-Topology-Updater, NFD creates CR intances corresponding to
node resource hardware topology such as:

 ```yaml
apiVersion: topology.node.k8s.io/v1alpha1
kind: NodeResourceTopology
metadata:
  name: node1
topologyPolicies: ["SingleNUMANodeContainerLevel"]
zones:
  - name: node-0
    type: Node
    resources:
      - name: cpu
        capacity: 20
        allocatable: 16
        available: 10
      - name: vendor/nic1
        capacity: 3
        allocatable: 3
        available: 3
  - name: node-1
    type: Node
    resources:
      - name: cpu
        capacity: 30
        allocatable: 30
        available: 15
      - name: vendor/nic2
        capacity: 6
        allocatable: 6
        available: 6
  - name: node-2
    type: Node
    resources:
      - name: cpu
        capacity: 30
        allocatable: 30
        available: 15
      - name: vendor/nic1
        capacity: 3
        allocatable: 3
        available: 3
 ```