Add config file support

Support yaml/json based config file for nfd. This commit does not add
any actual consumers for the config file, yet.

By default, nfd tries to read
/etc/kubernetes/node-feature-discovery/node-feature-discovery.conf.
This can be changed by specifying the --config command line flag.

Dockerfile

@@ -26,6 +26,7 @@ RUN glide install --strip-vendor
 RUN go install \
   -ldflags "-s -w -X main.version=$NFD_VERSION" \
   github.com/kubernetes-incubator/node-feature-discovery
+RUN install -D -m644 node-feature-discovery.conf.example /etc/kubernetes/node-feature-discovery/node-feature-discovery.conf
 
 RUN go test .
 
@@ -35,6 +36,7 @@ FROM debian:stretch-slim
 
 COPY --from=builder /usr/local/bin /usr/local/bin
 COPY --from=builder /usr/local/lib /usr/local/lib
+COPY --from=builder /etc/kubernetes/node-feature-discovery /etc/kubernetes/node-feature-discovery
 RUN ldconfig
 COPY --from=builder /go/bin/node-feature-discovery /usr/bin/node-feature-discovery
 

README.md

@@ -38,13 +38,15 @@ node-feature-discovery.
 
   Usage:
   node-feature-discovery [--no-publish] [--sources=<sources>] [--label-whitelist=<pattern>]
-     [--oneshot | --sleep-interval=<seconds>]
+     [--oneshot | --sleep-interval=<seconds>] [--config=<path>]
   node-feature-discovery -h | --help
   node-feature-discovery --version
 
   Options:
   -h --help                   Show this screen.
   --version                   Output version and exit.
+  --config=<path>             Config file to use.
+                              [Default: /etc/kubernetes/node-feature-discovery/node-feature-discovery.conf]
   --sources=<sources>         Comma separated list of feature sources.
                               [Default: cpuid,iommu,memory,network,pstate,rdt,selinux,storage]
   --no-publish                Do not publish discovered features to the
@@ -231,6 +233,43 @@ For example, if some node is tainted NoSchedule or fails to start a job for some
 
 [![asciicast](https://asciinema.org/a/11wir751y89617oemwnsgli4a.png)](https://asciinema.org/a/11wir751y89617oemwnsgli4a)
 
+### Configuration file
+
+NFD supports a configuration file. The default location is
+`/etc/kubernetes/node-feature-discovery/node-feature-discovery.conf`, but,
+this can be changed by specifying the`--config` command line flag. The file is
+read inside the Docker image, and thus, Volumes and VolumeMounts are needed to
+make your configuration available for NFD. The preferred method is to use a
+ConfigMap.
+For example, create a config map using the example config as a template:
+```
+cp node-feature-discovery.conf.example node-feature-discovery.conf
+vim node-feature-discovery.conf  # edit the configuration
+kubectl create configmap node-feature-discovery-config --from-file=node-feature-discovery.conf
+```
+Then, configure Volumes and VolumeMounts in the Pod spec (just the relevant
+snippets shown below):
+```
+...
+  containers:
+      volumeMounts:
+        - name: node-feature-discovery-config
+          mountPath: "/etc/kubernetes/node-feature-discovery/"
+...
+  volumes:
+    - name: node-feature-discovery-config
+      configMap:
+        name: node-feature-discovery-config
+...
+```
+You could also use other types of volumes, of course. That is, hostPath if
+different config for different nodes would be required, for example.
+
+The (empty-by-default)
+[example config](https://github.com/kubernetes-incubator/node-feature-discovery/blob/master/node-feature-discovery.conf.example)
+is used as a config in the NFD Docker image. Thus, this can be used as default
+configuration in custom-built images.
+
 ## Building from source
 
 Download the source code.

main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"io/ioutil"
 	"log"
 	"os"
 	"regexp"
@@ -9,6 +10,7 @@ import (
 	"time"
 
 	"github.com/docopt/docopt-go"
+	"github.com/ghodss/yaml"
 	"github.com/kubernetes-incubator/node-feature-discovery/source"
 	"github.com/kubernetes-incubator/node-feature-discovery/source/cpuid"
 	"github.com/kubernetes-incubator/node-feature-discovery/source/fake"
@@ -48,6 +50,14 @@ var (
 	stderrLogger = log.New(os.Stderr, "", log.LstdFlags)
 )
 
+// Global config
+type NFDConfig struct {
+	Sources struct {
+	} `json:"sources,omitempty"`
+}
+
+var config = NFDConfig{}
+
 // Labels are a Kubernetes representation of discovered features.
 type Labels map[string]string
 
@@ -76,6 +86,7 @@ type APIHelpers interface {
 // Command line arguments
 type Args struct {
 	labelWhiteList string
+	configFile     string
 	noPublish      bool
 	oneshot        bool
 	sleepInterval  time.Duration
@@ -91,6 +102,12 @@ func main() {
 	// Parse command-line arguments.
 	args := argsParse(nil)
 
+	// Read the config file
+	err := configParse(args.configFile)
+	if err != nil {
+		stderrLogger.Print(err)
+	}
+
 	// Configure the parameters for feature discovery.
 	enabledSources, labelWhiteList, err := configureParameters(args.sources, args.labelWhiteList)
 	if err != nil {
@@ -129,13 +146,15 @@ func argsParse(argv []string) (args Args) {
 
   Usage:
   %s [--no-publish] [--sources=<sources>] [--label-whitelist=<pattern>]
-     [--oneshot | --sleep-interval=<seconds>]
+     [--oneshot | --sleep-interval=<seconds>] [--config=<path>]
   %s -h | --help
   %s --version
 
   Options:
   -h --help                   Show this screen.
   --version                   Output version and exit.
+  --config=<path>             Config file to use.
+                              [Default: /etc/kubernetes/node-feature-discovery/node-feature-discovery.conf]
   --sources=<sources>         Comma separated list of feature sources.
                               [Default: cpuid,iommu,memory,network,pstate,rdt,selinux,storage]
   --no-publish                Do not publish discovered features to the
@@ -157,6 +176,7 @@ func argsParse(argv []string) (args Args) {
 
 	// Parse argument values as usable types.
 	var err error
+	args.configFile = arguments["--config"].(string)
 	args.noPublish = arguments["--no-publish"].(bool)
 	args.sources = strings.Split(arguments["--sources"].(string), ",")
 	args.labelWhiteList = arguments["--label-whitelist"].(string)
@@ -175,6 +195,22 @@ func argsParse(argv []string) (args Args) {
 	return args
 }
 
+// Parse configuration file
+func configParse(filepath string) error {
+	data, err := ioutil.ReadFile(filepath)
+	if err != nil {
+		return fmt.Errorf("Failed to read config file: %s", err)
+	}
+
+	// Read config file
+	err = yaml.Unmarshal(data, &config)
+	if err != nil {
+		return fmt.Errorf("Failed to parse config file: %s", err)
+	}
+
+	return nil
+}
+
 // configureParameters returns all the variables required to perform feature
 // discovery based on command line arguments.
 func configureParameters(sourcesWhiteList []string, labelWhiteListStr string) (enabledSources []source.FeatureSource, labelWhiteList *regexp.Regexp, err error) {

main_test.go

@@ -2,6 +2,8 @@ package main
 
 import (
 	"fmt"
+	"io/ioutil"
+	"os"
 	"regexp"
 	"testing"
 	"time"
@@ -174,6 +176,32 @@ func TestArgsParse(t *testing.T) {
 	})
 }
 
+func TestConfigParse(t *testing.T) {
+	Convey("When parsing configuration file", t, func() {
+		Convey("When non-accessible file is given", func() {
+			err := configParse("non-existing-file")
+
+			Convey("Should return error", func() {
+				So(err, ShouldNotBeNil)
+			})
+		})
+		// Create a temporary config file
+		f, err := ioutil.TempFile("", "nfd-test-")
+		defer os.Remove(f.Name())
+		So(err, ShouldBeNil)
+		f.WriteString(`sources:`)
+		f.Close()
+
+		Convey("When proper config file is given", func() {
+			err := configParse(f.Name())
+
+			Convey("Should return error", func() {
+				So(err, ShouldBeNil)
+			})
+		})
+	})
+}
+
 func TestConfigureParameters(t *testing.T) {
 	Convey("When configuring parameters for node feature discovery", t, func() {
 

node-feature-discovery.conf.example

@@ -0,0 +1 @@
+#sources: