cmd/kubernetes-static: use go:embed for serving static data

This way, binary is independent from host file system and it's only
important during build.

Signed-off-by: Mateusz Gozdek <mgozdek@microsoft.com>

cmd/kubernetes-static/main.go

@@ -1,8 +1,9 @@
 package main
 
 import (
-	"errors"
+	"embed"
 	"fmt"
+	"io/fs"
 	"net"
 	"net/http"
 	"os"
@@ -37,15 +38,19 @@ type argumentList struct {
 
 var args argumentList
 
-func main() {
+// Embed static metrics into binary.
+//go:embed data
+var content embed.FS
 
+func main() {
 	// Determines which subdirectory of cmd/kubernetes-static/ to use
 	// for serving the static metrics
 	k8sMetricsVersion := os.Getenv("K8S_METRICS_VERSION")
 	if k8sMetricsVersion == "" {
 		k8sMetricsVersion = "1_18"
 	}
-	endpoint := startStaticMetricsServer(k8sMetricsVersion)
+
+	endpoint := startStaticMetricsServer(content, k8sMetricsVersion)
 
 	// let the http server start...
 	time.Sleep(time.Millisecond * 100)
@@ -149,7 +154,7 @@ func main() {
 	fmt.Println()
 }
 
-func startStaticMetricsServer(k8sMetricsVersion string) string {
+func startStaticMetricsServer(content embed.FS, k8sMetricsVersion string) string {
 	// This will allocate a random port
 	listener, err := net.Listen("tcp", "127.0.0.1:0")
 	if err != nil {
@@ -161,14 +166,12 @@ func startStaticMetricsServer(k8sMetricsVersion string) string {
 
 	mux := http.NewServeMux()
 
-	dataDir := fmt.Sprintf("./cmd/kubernetes-static/data/%s", k8sMetricsVersion)
-
-	path, err := filepath.Abs(dataDir)
+	k8sContent, err := fs.Sub(content, filepath.Join("data", k8sMetricsVersion))
 	if err != nil {
-		log.Fatal(errors.New("cannot start server"))
+		panic(err)
 	}
 
-	mux.Handle("/", http.FileServer(http.Dir(path)))
+	mux.Handle("/", http.FileServer(http.FS(k8sContent)))
 	go func() {
 		logrus.Fatal(http.Serve(listener, mux))
 	}()

cmd/kubernetes-static/readme.md

@@ -15,14 +15,3 @@ go run cmd/kubernetes-static/main.go cmd/kubernetes-static/basic_http_client.go
 ```
 
 This is not sending any data to an agent, but outputs the JSON to stdout.
-
-## Configuring your IDE
-
-It's import that the working directory is set to root of the repository, because it expects the `data` folder to be
-in the `cmd/kubernetes-static` directory relative to the working directory.
-
-Some IDE's/editor use a temporary folder as the working directory.
-
-Example configuration for GoLand:
-![Goland configuration example](./config_example.png)
-