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code/images/sidecar/Dockerfile

@@ -0,0 +1,11 @@
+FROM golang:1.20 as builder
+WORKDIR /app
+COPY . .
+RUN go build
+
+FROM ubuntu
+RUN apt-get update && apt-get install -y dnsutils
+WORKDIR /app
+COPY --from=builder /app .
+EXPOSE 42069
+CMD /app/sidecar

code/images/sidecar/go.mod

@@ -0,0 +1,3 @@
+module iluzio.nicco.io/sidecar
+
+go 1.20

code/images/sidecar/main.go

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+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"os/exec"
+	"strings"
+)
+
+var SERVICE = os.Getenv("SERVICE")
+
+func getIPs() []string {
+	out, err := exec.Command("dig", "+short", "+search", SERVICE).Output()
+	if err != nil {
+		log.Fatal(err)
+		return []string{}
+	}
+
+	trimmed := strings.TrimSpace(fmt.Sprintf("%s", out))
+	if trimmed == "" {
+		return []string{}
+	} else {
+		return strings.Split(trimmed, "\n")
+	}
+}
+
+func main() {
+	http.HandleFunc("/discoverable", func(w http.ResponseWriter, r *http.Request) {
+		ips := getIPs()
+		plain := r.URL.Query().Get("format") == "plain"
+		if plain {
+			fmt.Fprintf(w, "%s\n", strings.Join(ips, "\n"))
+		} else {
+			w.Header().Set("Content-Type", "application/json")
+			json.NewEncoder(w).Encode(ips)
+		}
+	})
+
+	log.Fatal(http.ListenAndServe(":42069", nil))
+
+}