Support templating of label names in feature rules. It is available both
in NodeFeatureRule CRs and in custom rule configuration of nfd-worker.
This patch adds a new 'labelsTemplate' field to the rule spec, making it
possible to dynamically generate multiple labels per rule based on the
matched features. The feature relies on the golang "text/template"
package. When expanded, the template must contain labels in a raw
<key>[=<value>] format (where 'value' defaults to "true"), separated by
newlines i.e.:
- name: <rule-name>
labelsTemplate: |
<label-1>[=<value-1>]
<label-2>[=<value-2>]
...
All the matched features of 'matchFeatures' directives are available for
templating engine in a nested data structure that can be described in
yaml as:
.
<domain-1>:
<key-feature-1>:
- Name: <matched-key>
- ...
<value-feature-1:
- Name: <matched-key>
Value: <matched-value>
- ...
<instance-feature-1>:
- <attribute-1-name>: <attribute-1-value>
<attribute-2-name>: <attribute-2-value>
...
- ...
<domain-2>:
...
That is, the per-feature data available for matching depends on the type
of feature that was matched:
- "key features": only 'Name' is available
- "value features": 'Name' and 'Value' can be used
- "instance features": all attributes of the matched instance are
available
NOTE: In case of matchAny is specified, the template is executed
separately against each individual matchFeatures matcher and the
eventual set of labels is a superset of all these expansions. Consider
the following:
- name: <name>
labelsTemplate: <template>
matchAny:
- matchFeatures: <matcher#1>
- 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 and/or matcher#2 (depending on
whether both or only one of them match), and finally on matcher#3, and
all the labels from these separate expansions would be created (i.e. the
end result would be a union of all the individual expansions).
NOTE 2: The 'labels' field has priority over 'labelsTemplate', i.e.
labels specified in the 'labels' field will override any labels
originating from the 'labelsTemplate' field.
A special case of an empty match expression set matches everything (i.e.
matches/returns all existing keys/values). This makes it simpler to
write templates that run over all values. Also, makes it possible to
later implement support for templates that run over all _keys_ of a
feature.
Some example configurations:
- name: "my-pci-template-features"
labelsTemplate: |
{{ range .pci.device }}intel-{{ .class }}-{{ .device }}=present
{{ end }}
matchFeatures:
- feature: pci.device
matchExpressions:
class: {op: InRegexp, value: ["^06"]}
vendor: ["8086"]
- name: "my-system-template-features"
labelsTemplate: |
{{ range .system.osrelease }}system-{{ .Name }}={{ .Value }}
{{ end }}
matchFeatures:
- feature: system.osRelease
matchExpressions:
ID: {op: Exists}
VERSION_ID.major: {op: Exists}
Imaginative template pipelines are possible, of course, but care must be
taken in order to produce understandable and maintainable rule sets.
Create a new package pkg/apis/nfd/v1alpha1 and migrate the custom rule
expressions over there. This is the first step in creating a new CRD API
for custom rules.
