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README: better document the usage of hooks and feature files

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Mention supported runtimes that the hooks can use and describe how hooks
and feature files can be used for injecting labels from other pods.
This commit is contained in:
Markus Lehtonen 2020-02-11 16:24:28 +02:00
parent f6d119d85e
commit b7cc69fc80
1 changed files with 20 additions and 4 deletions
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README.md
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@ -335,8 +335,11 @@ feature sources.
The *local* feature source gets its labels by two different ways:
* It tries to execute files found under `/etc/kubernetes/node-feature-discovery/source.d/`
directory. The hook files must be executable. When executed, the hooks are
supposed to print all discovered features in `stdout`, one per line.
directory. The hook files must be executable and they are supposed to print all
discovered features in `stdout`, one per line. 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 stock image are bash and perl.
* It reads files found under `/etc/kubernetes/node-feature-discovery/features.d/`
directory. The file content is expected to be similar to the hook output (described above).
@ -368,7 +371,20 @@ label `my.namespace.org/my-label=value`, your hook output or file must contains
`stderr` output of the hooks is propagated to NFD log so it can be used for
debugging and logging.
**A hook example:**<br/>
#### 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. It is possible to mount
the `source.d` and/or `features.d` directories common with the NFD Pod and
deploy the custom hooks/features there. NFD will periodically scan the
directories and run any hooks and read any feature files it finds. The
[example nfd-worker deployment template](https://github.com/kubernetes-sigs/node-feature-discovery/blob/master/nfd-worker-daemonset.yaml.template#L69)
contains `hostPath` mounts for `sources.d` and `features.d` directories. By
using the same mounts in the secondary Pod (e.g. device plugin) you have
created a shared area for delivering hooks and feature files to NFD.
#### A Hook Example
User has a shell script
`/etc/kubernetes/node-feature-discovery/source.d/my-source` which has the
following `stdout` output:
@ -388,7 +404,7 @@ feature.node.kubernetes.io/override_source-OVERRIDE_VALUE=123
override.namespace/value=456
```
**A file example:**<br/>
#### A File Example
User has a file
`/etc/kubernetes/node-feature-discovery/features.d/my-source` which contains the
following lines: