metropolis/node/kubernetes/metricsproxy: clarify error message

If the metricsproxy fails to reach its target, we should not return the
same error message as the metrics service as that would be confusing.

Change-Id: Ia158686d5a7db3e8e62e149a1c7dc8773702a233
Reviewed-on: https://review.monogon.dev/c/monogon/+/2912
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
Tested-by: Jenkins CI
diff --git a/metropolis/node/kubernetes/metricsproxy/metricsproxy.go b/metropolis/node/kubernetes/metricsproxy/metricsproxy.go
index 02bce4b..bc44a34 100644
--- a/metropolis/node/kubernetes/metricsproxy/metricsproxy.go
+++ b/metropolis/node/kubernetes/metricsproxy/metricsproxy.go
@@ -84,7 +84,7 @@
 	res, err := s.transport.RoundTrip(outReq)
 	if err != nil {
 		logger.Errorf("%s: forwarding to %q failed: %v", r.RemoteAddr, s.Name, err)
-		http.Error(w, "could not reach exporter", http.StatusBadGateway)
+		http.Error(w, "could not reach endpoint", http.StatusBadGateway)
 		return
 	}
 	defer res.Body.Close()