feat: enable sd_notify support (#277)

backend/internal/utils/systemd/sdnotify.go

@@ -0,0 +1,33 @@
+package systemd
+
+import (
+	"net"
+	"os"
+)
+
+// SdNotifyReady sends a message to the systemd daemon to notify that service is ready to operate.
+// It is common to ignore the error.
+func SdNotifyReady() error {
+	socketAddr := &net.UnixAddr{
+		Name: os.Getenv("NOTIFY_SOCKET"),
+		Net:  "unixgram",
+	}
+
+	if socketAddr.Name == "" {
+		return nil
+	}
+
+	conn, err := net.DialUnix(socketAddr.Net, nil, socketAddr)
+	if err != nil {
+		return err
+	}
+	defer func() {
+		_ = conn.Close()
+	}()
+
+	if _, err = conn.Write([]byte("READY=1")); err != nil {
+		return err
+	}
+
+	return nil
+}