---
title: "Customization guide"
layout: default
sort: 5
---

# Customization guide
{: .no_toc}

## Table of contents
{: .no_toc .text-delta}

1. TOC
{:toc}

---

## Overview

NFD provides multiple extension points for vendor and application specific
labeling:

- [`NodeFeatureRule`](#nodefeaturerule-custom-resource) objects provide a way to
  deploy custom labeling rules via the Kubernetes API
- [`local`](#local-feature-source) feature source of nfd-worker creates
  labels by executing hooks and reading files
- [`custom`](#custom-feature-source) feature source of nfd-worker creates
  labels based on user-specified rules

## NodeFeatureRule custom resource

`NodeFeatureRule` objects provide an easy way to create vendor or application
specific labels. It uses a flexible rule-based mechanism for creating labels
based on node feature.

### A NodeFeatureRule example

Consider the following referential example:

```yaml
apiVersion: nfd.k8s-sigs.io/v1alpha1
kind: NodeFeatureRule
metadata:
  name: my-sample-rule-object
spec:
  rules:
    - name: "my sample rule"
      labels:
        "my-sample-feature": "true"
      matchFeatures:
        - feature: kernel.loadedmodule
          matchExpressions:
            dummy: {op: Exists}
        - feature: kernel.config
          matchExpressions:
            X86: {op: In, value: ["y"]}
```

It specifies one rule which creates node label
`feature.node.kubenernetes.io/my-sample-feature=true` if both of the following
conditions are true (`matchFeatures` implements a logical AND over the
matchers):

- The `dummy` network driver module has been loaded
- X86 option in kernel config is set to `=y`

Create a `NodeFeatureRule` with a yaml file:

```bash
kubectl apply -f https://raw.githubusercontent.com/kubernetes-sigs/node-feature-discovery/{{ site.release }}/examples/nodefeaturerule.yaml
```

Now, on X86 platforms the feature label appears after doing `modprobe dummy` on
a system and correspondingly the label is removed after `rmmod dummy`. Note a
re-labeling delay up to the sleep-interval of nfd-worker (1 minute by default).

### NodeFeatureRule controller

NFD-Master acts as the controller for `NodeFeatureRule` objects. It applies these
rules on raw feature data received from nfd-worker instances and creates node
labels, accordingly.

**NOTE** nfd-master is stateless and (re-)labelling only happens when a request
is received from nfd-worker. That is, in practice rules are evaluated and
labels for each node are created on intervals specified by the
[`core.sleepInterval`](worker-configuration-reference#coresleepinterval)
configuration option (or
[`-sleep-interval`](worker-commandline-reference#-sleep-interval) command line
flag) of nfd-worker instances. This means that modification or creation of
`NodeFeatureRule` objects does not instantly cause the node labels to be updated.
Instead, the changes only come visible in node labels as nfd-worker instances
send their labelling requests.

## Local feature source

NFD-Worker has a special feature source named `local` which is an integration
point for external feature detectors. It provides a mechanism for pluggable
extensions, allowing the creation of new user-specific features and even
overriding built-in labels.

The `local` feature source has two methods for detecting features, hooks and
feature files. The features discovered by the `local` source can further be
used in label rules specified in
[`NodeFeatureRule`](#nodefeaturerule-custom-resource) objects and the
[`custom`](#custom-feature-source) feature source.

**NOTE:** Be careful when creating and/or updating hook or feature files while
NFD is running. In order to avoid race conditions you should write into a
temporary file (outside the `source.d` and `features.d` directories), and,
atomically create/update the original file by doing a filesystem move
operation.

### A hook example

Consider a shell script
`/etc/kubernetes/node-feature-discovery/source.d/my-hook.sh` having the
following stdout output, or alternatively, a plaintext file
`/etc/kubernetes/node-feature-discovery/features.d/my-features` having the
following contents:

```plaintext
my-feature.1
my-feature.2=myvalue
my.namespace/my-feature.3=456
```

This will translate into the following node labels:

```yaml
feature.node.kubernetes.io/my-feature.1: "true"
feature.node.kubernetes.io/my-feature.2: "myvalue"
my.namespace/my-feature.3: "456"
```

Note that in the example above `-extra-label-ns=my.namespace` must be specified
on the nfd-master command line.

### Hooks

The `local` source executes hooks found in
`/etc/kubernetes/node-feature-discovery/source.d/`. The hook files must be
executable and they are supposed to print all discovered features in `stdout`.
With ELF binaries static linking is recommended as the selection of system
libraries available in the NFD release image is very limited. Other runtimes
currently supported by the NFD image are bash and perl.

`stderr` output of hooks is propagated to NFD log so it can be used for
debugging and logging.

NFD tries to execute any regular files found from the hooks directory.
Any additional data files the hook might need (e.g. a configuration file)
should be placed in a separate directory in order to avoid NFD unnecessarily
trying to execute them. A subdirectory under the hooks directory can be used,
for example `/etc/kubernetes/node-feature-discovery/source.d/conf/`.

**NOTE:** NFD will blindly run any executables placed/mounted in the hooks
directory. It is the user's responsibility to review the hooks for e.g.
possible security implications.

**NOTE:** The [minimal](../get-started/deployment-and-usage#minimal) image
variant only supports running statically linked binaries.

### Feature files

The `local` source reads files found in
`/etc/kubernetes/node-feature-discovery/features.d/`.

### Input format

The hook stdout and feature files are expected to contain features in simple
key-value pairs, separated by newlines:

```plaintext
<name>[=<value>]
```

The label value defaults to `true`, if not specified.

Label namespace may be specified with `<namespace>/<name>[=<value>]`. The
namespace must be explicitly allowed with the `-extra-label-ns` command line
flag of nfd-master if using something else than
`[<sub-ns>.]feature.node.kubernetes.io` or
`[<sub-ns>.]profile.node.kubernetes.io`.

### Mounts

The standard NFD deployments contain `hostPath` mounts for
`/etc/kubernetes/node-feature-discovery/source.d/` and
`/etc/kubernetes/node-feature-discovery/features.d/`, making these directories
from the host available inside the nfd-worker container.

#### Injecting labels from other pods

One use case for the hooks and/or feature files is detecting features in other
Pods outside NFD, e.g. in Kubernetes device plugins. By using the same
`hostPath` mounts for `/etc/kubernetes/node-feature-discovery/source.d/` and
`/etc/kubernetes/node-feature-discovery/features.d/` in the side-car (e.g.
device plugin) creates a shared area for deploying hooks and feature files to
NFD. NFD will periodically scan the directories and run any hooks and read any
feature files it finds.

## Custom feature source

The `custom` feature source in nfd-worker provides a rule-based mechanism for
label creation, similar to the
[`NodeFeatureRule`](#nodefeaturerule-custom-resource) objects. The difference is
that the rules are specified in the worker configuration instead of a
Kubernetes API object.

See [worker configuration](../get-started/deployment-and-usage.md#worker-configuration)
for instructions how to set-up and manage the worker configuration.

### An example custom feature source configuration

Consider the following referential configuration for nfd-worker:

```yaml
core:
  labelSources: ["custom"]
sources:
  custom:
    - name: "my sample rule"
      labels:
        "my-sample-feature": "true"
      matchFeatures:
        - feature: kernel.loadedmodule
          matchExpressions:
            dummy: {op: Exists}
        - feature: kernel.config
          matchExpressions:
            X86: {op: In, value: ["y"]}
```

It specifies one rule which creates node label
`feature.node.kubenernetes.io/my-sample-feature=true` if both of the following
conditions are true (`matchFeatures` implements a logical AND over the
matchers):

- The `dummy` network driver module has been loaded
- X86 option in kernel config is set to `=y`

In addition, the configuration only enables the `custom` source, disabling all
built-in labels.

Now, on X86 platforms the feature label appears after doing `modprobe dummy` on
a system and correspondingly the label is removed after `rmmod dummy`. Note a
re-labeling delay up to the sleep-interval of nfd-worker (1 minute by default).

### Additional configuration directory

In addition to the rules defined in the nfd-worker configuration file, the
`custom` feature source can read more configuration files located in the
`/etc/kubernetes/node-feature-discovery/custom.d/` directory. This makes more
dynamic and flexible configuration easier.

As an example, consider having file
`/etc/kubernetes/node-feature-discovery/custom.d/my-rule.yaml` with the
following content:

```yaml
- name: "my e1000 rule"
  labels:
    "e1000.present": "true"
  matchFeatures:
    - feature: kernel.loadedmodule
      matchExpressions:
        e1000: {op: Exists}
```

This simple rule will create `feature.node.kubenernetes.io/e1000.present=true`
label if the `e1000` kernel module has been loaded.

The
[`samples/custom-rules`](https://github.com/kubernetes-sigs/node-feature-discovery/blob/{{site.release}}/deployment/overlays/samples/custom-rules)
kustomize overlay sample contains an example for deploying a custom rule from a
ConfigMap.

## Node labels

Feature labels have the following format:

```plaintext
<namespace>/<name> = <value>
```

The namespace part (i.e. prefix) of the labels is controlled by nfd:

- All built-in labels use `feature.node.kubernetes.io`. This is also
  the default for user defined features that don't specify any namespace.
- User-defined labels are allowed to use:
  - `feature.node.kubernetes.io` and `profile.node.kubernetes.io` plus their
    sub-namespaces (e.g. `vendor.profile.node.kubernetes.io` and
    `sub.ns.profile.node.kubernetes.io`) by default
  - Additional namespaces may be enabled with the
    [`-extra-label-ns`](../advanced/master-commandline-reference#-extra-label-ns)
    command line flag of nfd-master

## Label rule format

This section describes the rule format used  in
[`NodeFeatureRule`](#nodefeaturerule-custom-resource) objects and in the
configuration of the [`custom`](#custom-feature-source) feature source.

It is based on a generic feature matcher that covers all features discovered by
nfd-worker. The rules rely on a unified data model of the available features
and a generic expression-based format. Features that can be used in the rules
are described in detail in [available features](#available-features) below.

Take this rule as a referential example:

```yaml
    - name: "my feature rule"
      labels:
        "my-special-feature": "my-value"
      matchFeatures:
        - feature: cpu.cpuid
          matchExpressions:
            AVX512F: {op: Exists}
        - feature: kernel.version
          matchExpressions:
            major: {op: In, value: ["5"]}
            minor: {op: Gt, value: ["1"]}
        - feature: pci.device
          matchExpressions:
            vendor: {op: In, value: ["8086"]}
            class: {op: In, value: ["0200"]}
```

This will yield `feature.node.kubenernetes.io/my-special-feature=my-value` node
label if all of these are true (`matchFeatures` implements a logical AND over
the matchers):

- the CPU has AVX512F capability
- kernel version is 5.2 or later (must be v5.x)
- an Intel network controller is present

### Fields

#### Name

The `.name` field is required and used as an identifier of the rule.

#### Labels

The `.labels` is a map of the node labels to create if the rule matches.

#### Labels template

The `.labelsTemplate` field specifies a text template for dynamically creating
labels based on the matched features. See [templating](#templating) for
details.

**NOTE** The `labels` field has priority over `labelsTemplate`, i.e.
labels specified in the `labels` field will override anything
originating from `labelsTemplate`.

#### Vars

The `.vars` field is a map of values (key-value pairs) to store for subsequent
rules to use. In other words, these are variables that are not advertised as
node labels. See [backreferences](#backreferences) for more details on the
usage of vars.

#### Vars template

The `.varsTemplate` field specifies a text template for dynamically creating
vars based on the matched features. See [templating](#templating) for details
on using templates and [backreferences](#backreferences) for more details on
the usage of vars.

**NOTE** The `vars` field has priority over `varsTemplate`, i.e.
vars specified in the `vars` field will override anything originating from
`varsTemplate`.

#### MatchFeatures

The `.matchFeatures` field specifies a feature matcher, consisting of a list of
feature matcher terms. It implements a logical AND over the terms i.e. all
of them must match in order for the rule to trigger.

```yaml
      matchFeatures:
        - feature: <feature-name>
          matchExpressions:
            <key>:
              op: <op>
              value:
                - <value-1>
                - ...
```

The `.matchFeatures[].feature` field specifies the feature against which to
match.

The `.matchFeatures[].matchExpressions` field specifies a map of expressions
which to evaluate against the elements of the feature.

In each MatchExpression `op` specifies the operator to apply. Valid values are
described below.

| Operator        | Number of values | Matches when
| --------------- | ---------------- | -----------
|  `In`           | 1 or greater | Input is equal to one of the values
|  `NotIn`        | 1 or greater | Input is not equal to any of the values
|  `InRegexp`     | 1 or greater | Values of the MatchExpression are treated as regexps and input matches one or more of them
|  `Exists`       | 0            | The key exists
|  `DoesNotExist` | 0            | The key does not exists
|  `Gt`           | 1            | Input is greater than the value. Both the input and value must be integer numbers.
|  `Lt`           | 1            | Input is less than the value. Both the input and value must be integer numbers.
|  `GtLt`         | 2            | Input is between two values. Both the input and value must be integer numbers.
|  `IsTrue`       | 0            | Input is equal to "true"
|  `IsFalse`      | 0            | Input is equal "false"

The `value` field of MatchExpression is a list of string arguments to the
operator.

The behavior of MatchExpression depends on the [feature type](#feature-types):
for *flag* and *attribute* features the MatchExpression operates on the feature
element whose name matches the `<key>`. However, for *instance* features all
MatchExpressions are evaluated against the attributes of each instance
separately.

#### MatchAny

The `.matchAny` field is a list of of [`matchFeatures`](#matchfeatures)
matchers. A logical OR is applied over the matchers, i.e. at least one of them
must match in order for the rule to trigger.

Consider the following example:

```yaml
      matchAny:
        - matchFeatures:
            - feature: kernel.loadedmodule
              matchExpressions:
                kmod-1: {op: Exists}
            - feature: pci.device
              matchExpressions:
                vendor: {op: In, value: ["0eee"]}
                class: {op: In, value: ["0200"]}
        - matchFeatures:
            - feature: kernel.loadedmodule
              matchExpressions:
                kmod-2: {op: Exists}
            - feature: pci.device
              matchExpressions:
                vendor: {op: In, value: ["0fff"]}
                class: {op: In, value: ["0200"]}
```

This matches if kernel module kmod-1 is loaded and a network controller from
vendor 0eee is present, OR, if kernel module kmod-2 has been loaded and a
network controller from vendor 0fff is present (OR both of these conditions are
true).

### Available features

#### Feature types

Features are divided into three different types:

- **flag** features: a set of names without any associated values, e.g. CPUID
  flags or loaded kernel modules
- **attribute** features: a set of names each of which has a single value
  associated with it (essentially a map of key-value pairs), e.g. kernel config
  flags or os release information
- **instance** features: a list of instances, each of which has multiple
  attributes (key-value pairs of their own) associated with it, e.g. PCI or USB
  devices

#### List of features

The following features are available for matching:

| Feature          | Feature type | Elements | Value type | Description
| ---------------- | ------------ | -------- | ---------- | -----------
| **`cpu.cpuid`**  | flag         |          |            | Supported CPU capabilities
|                  |              | **`<cpuid-flag>`** |  | CPUID flag is present
| **`cpu.cstate`** | attribute    |          |            | Status of cstates in the intel_idle cpuidle driver
|                  |              | **`enabled`** | bool  | 'true' if cstates are set, otherwise 'false'. Does not exist of intel_idle driver is not active.
| **`cpu.model`**  | attribute    |          |            | CPU model related attributes
|                  |              | **`family`** | int    | CPU family
|                  |              | **`vendor_id`** | string | CPU vendor ID
|                  |              | **`id`** | int        | CPU model ID
| **`cpu.pstate`** | attribute    |          |            | State of the Intel pstate driver. Does not exist if the driver is not enabled.
|                  |              | **`status`** | string | Status of the driver, possible values are 'active' and 'passive'
|                  |              | **`turbo`**  | bool   | 'true' if turbo frequencies are enabled, otherwise 'false'
|                  |              | **`scaling`** | string | Active scaling_governor, possible values are 'powersave' or 'performance'.
| **`cpu.rdt`**    | flag         |          |            | Intel RDT capabilities supported by the system
|                  |              | **`<rdt-flag>`** |    | RDT capability is supported, see [RDT flags](../get-started/features#intel-rdt-flags) for details
| **`cpu.sgx`**    | attribute    |          |            | Intel SGX (Software Guard Extensions) capabilities
|                  |              | **`enabled`** | bool  | `true` if Intel SGX has been enabled, otherwise does not exist
| **`cpu.sst`**    | attribute    |          |            | Intel SST (Speed Select Technology) capabilities
|                  |              | **`bf.enabled`** | bool | `true` if Intel SST-BF (Intel Speed Select Technology - Base frequency) has been enabled, otherwise does not exist
| **`cpu.se`**     | attribute    |          |            | IBM Secure Execution for Linux (IBM Z & LinuxONE)
|                  |              | **`enabled`** | bool  | `true` if IBM Secure Execution for Linux is available and has been enabled, otherwise does not exist
| **`cpu.topology`** | attribute  |          |            | CPU topology related features
| | |          **`hardware_multithreading`** | bool       | Hardware multithreading, such as Intel HTT, is enabled
| **`kernel.config`** | attribute |          |            | Kernel configuration options
|                  |              | **`<config-flag>`** | string | Value of the kconfig option
| **`kernel.loadedmodule`** | flag |         |            | Loaded kernel modules
|                  |              | **`mod-name`** |      | Kernel module `<mod-name>` is loaded
| **`kernel.selinux`** | attribute |         |            | Kernel SELinux related features
|                  |              | **`enabled`** | bool  | `true` if SELinux has been enabled and is in enforcing mode, otherwise `false`
| **`kernel.version`** | attribute |          |           | Kernel version information
|                  |              | **`full`** | string   | Full kernel version (e.g. ‘4.5.6-7-g123abcde')
|                  |              | **`major`** | int     | First component of the kernel version (e.g. ‘4')
|                  |              | **`minor`** | int     | Second component of the kernel version (e.g. ‘5')
|                  |              | **`revision`** | int  | Third component of the kernel version (e.g. ‘6')
| **`local.label`** | attribute   |           |           | Features from hooks and feature files, i.e. labels from the [*local* feature source](#local-feature-source)
|                  |              | **`<label-name>`** | string | Label `<label-name>` created by the local feature source, value equals the value of the label
| **`memory.nv`**  | instance     |          |            | NVDIMM devices present in the system
|                  |              | **`<sysfs-attribute>`** | string | Value of the sysfs device attribute, available attributes: `devtype`, `mode`
| **`memory.numa`**  | attribute  |          |            | NUMA nodes
|                  |              | **`is_numa`** | bool  | `true` if NUMA architecture, `false` otherwise
|                  |              | **`node_count`** | int | Number of NUMA nodes
| **`network.device`** | instance |          |            | Physical (non-virtual) network interfaces present in the system
|                  |              | **`name`** | string   | Name of the network interface
|                  |              | **`<sysfs-attribute>`** | string | Sysfs network interface attribute, available attributes: `operstate`, `speed`, `sriov_numvfs`, `sriov_totalvfs`
| **`pci.device`** | instance     |          |            | PCI devices present in the system
|                  |              | **`<sysfs-attribute>`** | string | Value of the sysfs device attribute, available attributes: `class`, `vendor`, `device`, `subsystem_vendor`, `subsystem_device`, `sriov_totalvfs`, `iommu_group/type`, `iommu/intel-iommu/version`
| **`storage.device`** | instance |          |            | Block storage devices present in the system
|                  |              | **`name`** | string   | Name of the block device
|                  |              | **`<sysfs-attribute>`** | string | Sysfs network interface attribute, available attributes: `dax`, `rotational`, `nr_zones`, `zoned`
| **`system.osrelease`** | attribute |          |            | System identification data from `/etc/os-release`
|                  |              | **`<parameter>`** | string | One parameter from `/etc/os-release`
| **`system.name`** | attribute   |          |            | System name information
|                  |              | **`nodename`** | string | Name of the kubernetes node object
| **`usb.device`** | instance     |          |            | USB devices present in the system
|                  |              | **`<sysfs-attribute>`** | string | Value of the sysfs device attribute, available attributes: `class`, `vendor`, `device`, `serial`
| **`rule.matched`** | attribute  |          |            | Previously matched rules
|                  |              | **`<label-or-var>`** | string | Label or var from a preceding rule that matched

### Templating

Rules support template-based creation of labels and vars with the
`.labelsTemplate` and `.varsTemplate` fields. These makes it possible to
dynamically generate labels and vars based on the features that matched.

The template must expand into a simple format with `<key>=<value>` pairs
separated by newline.

Consider the following example:
<!-- {% raw %} -->

```yaml
    labelsTemplate: |
      {{ range .pci.device }}vendor-{{ .class }}-{{ .device }}.present=true
      {{ end }}
    matchFeatures:
      - feature: pci.device
        matchExpressions:
          class: {op: InRegexp, value: ["^02"]}
          vendor: ["0fff"]
```

<!-- {% endraw %} -->
The rule above will create individual labels
`feature.node.kubernetes.io/vendor-<class-id>-<device-id>.present=true` for
each network controller device (device class starting with 02) from vendor
0ffff.

All the matched features of each feature matcher term under `matchFeatures`
fields are available for the template engine. Matched features can be
referenced with `{%raw%}{{ .<feature-name> }}{%endraw%}` in the template, and
the available data could be described in yaml as follows:

```yaml
.
  <key-feature>:
    - Name: <matched-key>
    - ...

  <value-feature>:
    - Name: <matched-key>
      Value: <matched-value>
    - ...

  <instance-feature>:
    - <attribute-1-name>: <attribute-1-value>
      <attribute-2-name>: <attribute-2-value>
      ...
    - ...
```

That is, the per-feature data is a list of objects whose data fields depend on
the type of the feature:

- for *flag* features only 'Name' is available
- for *value* features 'Name' and 'Value' are available
- for *instance* features all attributes of the matched instance are available

A simple example of a template utilizing name and value from an *attribute*
feature:
<!-- {% raw %} -->

```yaml
    labelsTemplate: |
      {{ range .system.osrelease }}system-{{ .Name }}={{ .Value }}
      {{ end }}
    matchFeatures:
      - feature: system.osRelease
        matchExpressions:
          ID: {op: Exists}
          VERSION_ID.major: {op: Exists}
```

<!-- {% endraw %} -->
**NOTE** In case of matchAny is specified, the template is executed separately
against each individual `matchFeatures` field and the final set of labels will
be superset of all these separate template expansions. E.g. consider the
following:

```yaml
  - name: <name>
    labelsTemplate: <template>
    matchFeatures: <matcher#1>
    matchAny:
      - matchFeatures: <matcher#2>
      - matchFeatures: <matcher#3>
```

In the example above (assuming the overall result is a match) the template
would be executed on matcher#1 as well as on matcher#2 and/or matcher#3
(depending on whether both or only one of them match). All the labels from
these separate expansions would be created, i.e. the end result would be a
union of all the individual expansions.

Rule templates use the Golang [text/template](https://pkg.go.dev/text/template)
package and all its built-in functionality (e.g. pipelines and functions) can
be used. An example template taking use of the built-in `len` function,
advertising the number of PCI network controllers from a specific vendor:
<!-- {% raw %} -->

```yaml
    labelsTemplate: |
      num-intel-network-controllers={{ .pci.device | len }}
    matchFeatures:
      - feature: pci.device
        matchExpressions:
          vendor: {op: In, value: ["8086"]}
          class: {op: In, value: ["0200"]}

```

<!-- {% endraw %} -->
Imaginative template pipelines are possible, but care must be taken in order to
produce understandable and maintainable rule sets.

### Backreferences

Rules support referencing the output of preceding rules. This enables
sophisticated scenarios where multiple rules are combined together
to for more complex heuristics than a single rule can provide. The labels and
vars created by the execution of preceding rules are available as a special
`rule.matched` feature.

Consider the following configuration:

```yaml
  - name: "my kernel label rule"
    labels:
      kernel-feature: "true"
    matchFeatures:
      - feature: kernel.version
        matchExpressions:
          major: {op: Gt, value: ["4"]}

  - name: "my var rule"
    vars:
      nolabel-feature: "true"
    matchFeatures:
      - feature: cpu.cpuid
        matchExpressions:
          AVX512F: {op: Exists}
      - feature: pci.device
        matchExpressions:
          vendor: {op: In, value: ["0fff"]}
          device: {op: In, value: ["1234", "1235"]}

  - name: "my high level feature rule"
    labels:
      high-level-feature: "true"
    matchFeatures:
      - feature: rule.matched
        matchExpressions:
          kernel-feature: {op: IsTrue}
          nolabel-feature: {op: IsTrue}
```

The `feature.node.kubernetes.io/high-level-feature = true` label depends on thw
two previous rules.

Note that when referencing rules across multiple
[`NodeFeatureRule`](#nodefeaturerule-custom-resource) objects attention must be
paid to the ordering. `NodeFeatureRule` objects are processed in alphabetical
order (based on their `.metadata.name`).

### Examples

Some more configuration examples below.

Match certain CPUID features:

```yaml
  - name: "example cpuid rule"
    labels:
      my-special-cpu-feature: "true"
    matchFeatures:
      - feature: cpu.cpuid
        matchExpressions:
          AESNI: {op: Exists}
          AVX: {op: Exists}
```

Require a certain loaded kernel module and OS version:

```yaml
  - name: "my multi-feature rule"
    labels:
      my-special-multi-feature: "true"
    matchFeatures:
      - feature: kernel.loadedmodule
        matchExpressions:
          e1000: {op: Exists}
      - feature: system.osrelease
        matchExpressions:
          NAME: {op: InRegexp, values: ["^openSUSE"]}
          VERSION_ID.major: {op: Gt, values: ["14"]}
```

Require a loaded  kernel module and two specific PCI devices (both of which
must be present):

```yaml
  - name: "my multi-device rule"
    labels:
      my-multi-device-feature: "true"
    matchFeatures:
      - feature: kernel.loadedmodule
        matchExpressions:
          my-driver-module: {op: Exists}
      - pci.device:
          vendor: "0fff"
          device: "1234"
      - pci.device:
          vendor: "0fff"
          device: "abcd"
```

## Legacy custom rule syntax

**DEPRECATED**: use the new rule syntax instead.

The `custom` source supports the legacy `matchOn` rule syntax for
backwards-compatibility.

To aid in making the legacy rule syntax clearer, we define a general and a per
rule nomenclature, keeping things as consistent as possible.

### General nomenclature and definitions

```plaintext
Rule        :Represents a matching logic that is used to match on a feature.
Rule Input  :The input a Rule is provided. This determines how a Rule performs the match operation.
Matcher     :A composition of Rules, each Matcher may be composed of at most one instance of each Rule.
```

### Custom features format (using the nomenclature defined above)

Rules are specified under `sources.custom` in the nfd-worker configuration
file.

```yaml
sources:
  custom:
  - name: <feature name>
    value: <optional feature value, defaults to "true">
    matchOn:
    - <Rule-1>: <Rule-1 Input>
      [<Rule-2>: <Rule-2 Input>]
    - <Matcher-2>
    - ...
    - ...
    - <Matcher-N>
  - <custom feature 2>
  - ...
  - ...
  - <custom feature M>
```

The label is constructed by adding `custom-` prefix to the name field, label
value defaults to `true` if not specified in the rule spec:

```plaintext
feature.node.kubernetes.io/custom-<name> = <value>
```

### Matching process

Specifying Rules to match on a feature is done by providing a list of Matchers.
Each Matcher contains one or more Rules.

Logical _OR_ is performed between Matchers and logical _AND_ is performed
between Rules of a given Matcher.

### Rules

#### pciid rule

##### Nomenclature

```plaintext
Attribute   :A PCI attribute.
Element     :An identifier of the PCI attribute.
```

The PciId Rule allows matching the PCI devices in the system on the following
Attributes: `class`,`vendor` and `device`. A list of Elements is provided for
each Attribute.

##### Format

```yaml
pciId :
  class: [<class id>, ...]
  vendor: [<vendor id>,  ...]
  device: [<device id>, ...]
```

Matching is done by performing a logical _OR_ between Elements of an Attribute
and logical _AND_ between the specified Attributes for each PCI device in the
system.  At least one Attribute must be specified. Missing attributes will not
partake in the matching process.

#### UsbId rule

##### Nomenclature

```plaintext
Attribute   :A USB attribute.
Element     :An identifier of the USB attribute.
```

The UsbId Rule allows matching the USB devices in the system on the following
Attributes: `class`,`vendor`, `device` and `serial`. A list of Elements is
provided for each Attribute.

##### Format

```yaml
usbId :
  class: [<class id>, ...]
  vendor: [<vendor id>,  ...]
  device: [<device id>, ...]
  serial: [<serial>, ...]
```

Matching is done by performing a logical _OR_ between Elements of an Attribute
and logical _AND_ between the specified Attributes for each USB device in the
system.  At least one Attribute must be specified. Missing attributes will not
partake in the matching process.

#### LoadedKMod rule

##### Nomenclature

```plaintext
Element     :A kernel module
```

The LoadedKMod Rule allows matching the loaded kernel modules in the system
against a provided list of Elements.

##### Format

```yaml
loadedKMod : [<kernel module>, ...]
```

Matching is done by performing logical _AND_ for each provided Element, i.e
the Rule will match if all provided Elements (kernel modules) are loaded in the
system.

#### CpuId rule

##### Nomenclature

```plaintext
Element     :A CPUID flag
```

The Rule allows matching the available CPUID flags in the system against a
provided list of Elements.

##### Format

```yaml
cpuId : [<CPUID flag string>, ...]
```

Matching is done by performing logical _AND_ for each provided Element, i.e the
Rule will match if all provided Elements (CPUID flag strings) are available in
the system.

#### Kconfig rule

##### Nomenclature

```plaintext
Element     :A Kconfig option
```

The Rule allows matching the kconfig options in the system against a provided
list of Elements.

##### Format

```yaml
kConfig: [<kernel config option ('y' or 'm') or '=<value>'>, ...]
```

Matching is done by performing logical _AND_ for each provided Element, i.e the
Rule will match if all provided Elements (kernel config options) are enabled
(`y` or `m`) or matching `=<value>` in the kernel.

#### Nodename rule

##### Nomenclature

```plaintext
Element     :A nodename regexp pattern
```

The Rule allows matching the node's name against a provided list of Elements.

##### Format

```yaml
nodename: [ <nodename regexp pattern>, ... ]
```

Matching is done by performing logical _OR_ for each provided Element, i.e the
Rule will match if one of the provided Elements (nodename regexp pattern)
matches the node's name.

### Legacy custom rule example

```yaml
custom:
  - name: "my.kernel.feature"
    matchOn:
      - loadedKMod: ["kmod1", "kmod2"]
  - name: "my.pci.feature"
    matchOn:
      - pciId:
          vendor: ["15b3"]
          device: ["1014", "1017"]
  - name: "my.usb.feature"
    matchOn:
      - usbId:
          vendor: ["1d6b"]
          device: ["0003"]
          serial: ["090129a"]
  - name: "my.combined.feature"
    matchOn:
      - loadedKMod : ["vendor_kmod1", "vendor_kmod2"]
        pciId:
          vendor: ["15b3"]
          device: ["1014", "1017"]
  - name: "vendor.feature.node.kubernetes.io/accumulated.feature"
    matchOn:
      - loadedKMod : ["some_kmod1", "some_kmod2"]
      - pciId:
          vendor: ["15b3"]
          device: ["1014", "1017"]
  - name: "my.kernel.featureneedscpu"
    matchOn:
      - kConfig: ["KVM_INTEL"]
      - cpuId: ["VMX"]
  - name: "my.kernel.modulecompiler"
    matchOn:
      - kConfig: ["GCC_VERSION=100101"]
        loadedKMod: ["kmod1"]
  - name: "profile.node.kubernetes.io/my-datacenter"
    value: "datacenter-1"
    matchOn:
      - nodename: [ "node-datacenter1-rack.*-server.*" ]
```

__In the example above:__

- A node would contain the label:
  `feature.node.kubernetes.io/custom-my.kernel.feature=true` if the node has
  `kmod1` _AND_ `kmod2` kernel modules loaded.
- A node would contain the label:
  `feature.node.kubernetes.io/custom-my.pci.feature=true` if the node contains
  a PCI device with a PCI vendor ID of `15b3` _AND_ PCI device ID of `1014` _OR_
  `1017`.
- A node would contain the label:
  `feature.node.kubernetes.io/custom-my.usb.feature=true` if the node contains
  a USB device with a USB vendor ID of `1d6b` _AND_ USB device ID of `0003`.
- A node would contain the label:
  `feature.node.kubernetes.io/custom-my.combined.feature=true` if
  `vendor_kmod1` _AND_ `vendor_kmod2` kernel modules are loaded __AND__ the node
  contains a PCI device
  with a PCI vendor ID of `15b3` _AND_ PCI device ID of `1014` _or_ `1017`.
- A node would contain the label:
  `vendor.feature.node.kubernetes.io/accumulated.feature=true` if
  `some_kmod1` _AND_ `some_kmod2` kernel modules are loaded __OR__ the node
  contains a PCI device
  with a PCI vendor ID of `15b3` _AND_ PCI device ID of `1014` _OR_ `1017`.
- A node would contain the label:
  `feature.node.kubernetes.io/custom-my.kernel.featureneedscpu=true` if
  `KVM_INTEL` kernel config is enabled __AND__ the node CPU supports `VMX`
  virtual machine extensions
- A node would contain the label:
  `feature.node.kubernetes.io/custom-my.kernel.modulecompiler=true` if the
  in-tree `kmod1` kernel module is loaded __AND__ it's built with
  `GCC_VERSION=100101`.
- A node would contain the label:
  `profile.node.kubernetes.io/my-datacenter=datacenter-1` if the node's name
  matches the `node-datacenter1-rack.*-server.*` pattern, e.g.
  `node-datacenter1-rack2-server42`