feat: Raspberry Pi hardware discovery for Node Feature Discovery

rpi-nfd-discovery/Dockerfile

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+FROM --platform=$BUILDPLATFORM golang:1.23-alpine AS build
+ARG TARGETOS=linux
+ARG TARGETARCH
+ARG TARGETVARIANT
+WORKDIR /src
+COPY go.mod main.go ./
+RUN CGO_ENABLED=0 GOOS=$TARGETOS GOARCH=$TARGETARCH GOARM=${TARGETVARIANT#v} go build -trimpath -ldflags="-s -w" -o /out/rpi-nfd-discovery .
+
+FROM scratch
+COPY --from=build /out/rpi-nfd-discovery /rpi-nfd-discovery
+USER 65532:65532
+ENTRYPOINT ["/rpi-nfd-discovery"]

rpi-nfd-discovery/PLATFORMS

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+linux/arm/v7
+linux/arm64
+linux/amd64

rpi-nfd-discovery/README.md

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+# Raspberry Pi NFD discovery
+
+Minimal Go-based Raspberry Pi hardware discovery for the Node Feature Discovery (NFD) `local` source.
+
+Reads the host's device-tree model and optional `/proc/cpuinfo` revision, and atomically writes an NFD feature file to `features.d/rpi`. Does **not** require Kubernetes API permissions. Does **not** update health/status labels on every sample.
+
+## Labels
+
+- `feature.node.kubernetes.io/rpi-present=true`
+- `feature.node.kubernetes.io/rpi-model=3-bplus` (model-dependent)
+- `feature.node.kubernetes.io/rpi-revision=a020d3` (if exposed by the kernel)
+
+## Requirements
+
+Your deployed NFD worker must have the `local` source enabled **and must mount the same host path** (`/etc/kubernetes/node-feature-discovery/features.d`) as this DaemonSet.
+
+Example local host test:
+
+```sh
+go test ./...
+go run . -model /proc/device-tree/model -cpuinfo /proc/cpuinfo \
+  -output /tmp/rpi-nfd-features -interval 5m
+```
+
+Build and publish the multi-arch image before enabling the draft homelab deployment:
+
+```sh
+docker buildx build --platform linux/arm/v7,linux/arm64,linux/amd64 \
+  -t davidcollom/rpi-nfd-discovery:0.1.0 --push .
+```
+
+Image is not published merely by committing these source files. The image is intentionally distroless/non-root. The DaemonSet needs a writable host-mounted NFD features directory.
+
+Throttling and undervoltage are deliberately out of scope for static NFD labels; they belong in Prometheus telemetry and alerts. A later exporter can expose `vcgencmd get_throttled` and associated events.

rpi-nfd-discovery/VERSION

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+0.1.0

rpi-nfd-discovery/go.mod

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+module github.com/davidcollom/dockerfiles/rpi-nfd-discovery
+
+go 1.23

rpi-nfd-discovery/main.go

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+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"time"
+)
+
+var safeValue = regexp.MustCompile(`[^a-z0-9.-]+`)
+
+func readModel(path string) (string, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return "", err
+	}
+	model := strings.TrimSpace(strings.TrimRight(string(data), "\x00"))
+	if !strings.HasPrefix(model, "Raspberry Pi ") {
+		return "", fmt.Errorf("not a Raspberry Pi: %q", model)
+	}
+	return model, nil
+}
+
+func modelID(model string) string {
+	name := strings.TrimPrefix(model, "Raspberry Pi ")
+	name = strings.TrimSpace(strings.Split(name, " Rev ")[0])
+	name = strings.ToLower(name)
+	name = strings.ReplaceAll(name, " Model ", " ")
+	name = strings.ReplaceAll(name, " Plus", "+")
+	name = strings.ReplaceAll(name, "+", "plus")
+	name = strings.ReplaceAll(name, " ", "-")
+	return strings.Trim(safeValue.ReplaceAllString(name, "-"), "-.")
+}
+
+func revision(path string) string {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return ""
+	}
+	for _, line := range strings.Split(string(data), "\n") {
+		if key, val, ok := strings.Cut(line, ":"); ok && strings.TrimSpace(key) == "Revision" {
+			value := strings.ToLower(strings.TrimSpace(val))
+			if regexp.MustCompile(`^[a-f0-9]+$`).MatchString(value) {
+				return value
+			}
+		}
+	}
+	return ""
+}
+
+func featureContent(model, rev string) string {
+	var b strings.Builder
+	fmt.Fprintln(&b, "# Automatically generated by rpi-nfd-discovery")
+	fmt.Fprintln(&b, "feature.node.kubernetes.io/rpi-present=true")
+	fmt.Fprintf(&b, "feature.node.kubernetes.io/rpi-model=%s\n", modelID(model))
+	if rev != "" {
+		fmt.Fprintf(&b, "feature.node.kubernetes.io/rpi-revision=%s\n", rev)
+	}
+	return b.String()
+}
+
+func writeAtomic(path, data string) error {
+	dir := filepath.Dir(path)
+	tmp, err := os.CreateTemp(dir, ".rpi-nfd-*")
+	if err != nil {
+		return err
+	}
+	defer os.Remove(tmp.Name())
+	if _, err := tmp.WriteString(data); err != nil {
+		tmp.Close()
+		return err
+	}
+	if err := tmp.Chmod(0644); err != nil {
+		tmp.Close()
+		return err
+	}
+	if err := tmp.Close(); err != nil {
+		return err
+	}
+	return os.Rename(tmp.Name(), path)
+}
+
+func main() {
+	modelPath := flag.String("model", "/host/device-tree/model", "host device-tree model file")
+	cpuInfoPath := flag.String("cpuinfo", "/host/cpuinfo", "host /proc/cpuinfo")
+	output := flag.String("output", "/features.d/rpi", "NFD local feature file")
+	interval := flag.Duration("interval", 5*time.Minute, "reconciliation interval")
+	flag.Parse()
+
+	if *interval <= 0 {
+		log.Fatal("interval must be positive")
+	}
+	for {
+		model, err := readModel(*modelPath)
+		if err != nil {
+			log.Printf("discovery failed: %v", err)
+		} else {
+			content := featureContent(model, revision(*cpuInfoPath))
+			old, err := os.ReadFile(*output)
+			if err != nil || string(old) != content {
+				if err := writeAtomic(*output, content); err != nil {
+					log.Printf("feature write failed: %v", err)
+				} else {
+					log.Printf("discovered %s (%s)", model, modelID(model))
+				}
+			}
+		}
+		time.Sleep(*interval)
+	}
+}

rpi-nfd-discovery/main_test.go

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+package main
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestModelID(t *testing.T) {
+	cases := map[string]string{
+		"Raspberry Pi 3 Model B Plus Rev 1.3": "3-bplus",
+		"Raspberry Pi 4 Model B Rev 1.4":      "4-b",
+		"Raspberry Pi 5 Model B Rev 1.0":      "5-b",
+		"Raspberry Pi 5 Rev 1.0":              "5",
+	}
+	for input, want := range cases {
+		if got := modelID(input); got != want {
+			t.Errorf("modelID(%q) = %q, want %q", input, got, want)
+		}
+	}
+}
+
+func TestReadModel(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "model")
+	if err := os.WriteFile(path, []byte("Raspberry Pi 3 Model B Plus Rev 1.3\x00"), 0600); err != nil {
+		t.Fatal(err)
+	}
+	model, err := readModel(path)
+	if err != nil || model != "Raspberry Pi 3 Model B Plus Rev 1.3" {
+		t.Fatalf("model=%q err=%v", model, err)
+	}
+}
+
+func TestNotRPi(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "model")
+	if err := os.WriteFile(path, []byte("Other Board\x00"), 0600); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := readModel(path); err == nil {
+		t.Fatal("expected an error")
+	}
+}
+
+func TestRevision(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "cpuinfo")
+	if err := os.WriteFile(path, []byte("Hardware : BCM2835\nRevision : a020d3\n"), 0600); err != nil {
+		t.Fatal(err)
+	}
+	if got := revision(path); got != "a020d3" {
+		t.Fatalf("revision=%q", got)
+	}
+}
+
+func TestAtomicOutput(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "rpi")
+	content := featureContent("Raspberry Pi 3 Model B Plus Rev 1.3", "a020d3")
+	if err := writeAtomic(path, content); err != nil {
+		t.Fatal(err)
+	}
+	got, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !strings.Contains(string(got), "rpi-model=3-bplus") {
+		t.Fatalf("unexpected features: %s", got)
+	}
+}