Extend the FeatureSource interface with new methods for configuration
handling. This enables easier on-the fly reconfiguration of the
feature sources. Further, it simplifies adding config support to feature
sources in the future. Stub methods are added to sources that do not
currently have any configurability.
The patch fixes some (corner) cases with the overrides (--options)
handling, too:
- Overrides were not applied if config file was missing or its parsing
failed
- Overrides for a certain source did not have effect if an empty config
for the source was specified in the config file. This was caused by
the first pass of parsing (config file) setting a nil pointer to the
source-specific config, effectively detaching it from the main config.
The second pass would then create a new instance of the source
specific config, but, this was not visible in the feature source, of
course.
Refactor NFD into a simple server-client system. Labeling is now done by
a separate 'nfd-master' server. It is a simple service with small
codebase, designed for easy isolation. The feature discovery part is
implemented in a 'nfd-worker' client which sends labeling requests to
nfd-server, thus, requiring no access/permissions to the Kubernetes API
itself.
Client-server communication is implemented by using gRPC. The protocol
currently consists of only one request, i.e. the labeling request.
The spec templates are converted to the new scheme. The nfd-master
server can be deployed using the nfd-master.yaml.template which now also
contains the necessary RBAC configuration. NFD workers can be deployed
by using the nfd-worker-daemonset.yaml.template or
nfd-worker-job.yaml.template (most easily used with the label-nodes.sh
script).
Only nfd-worker currently support config file or options. The (default)
NFD config file is renamed to nfd-worker.conf.
