fix the opentelemetry setup

Signed-off-by: Fredrik Adelöw <freben@gmail.com>

packages/backend/src/instrumentation.js

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2024 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+const { NodeSDK } = require('@opentelemetry/sdk-node');
+const {
+  getNodeAutoInstrumentations,
+} = require('@opentelemetry/auto-instrumentations-node');
+const { PrometheusExporter } = require('@opentelemetry/exporter-prometheus');
+
+// Expose opentelemetry metrics using a Prometheus exporter on
+// http://localhost:9464/metrics. See packages/backend/prometheus.yml for
+// more information on how to scrape it.
+const prometheus = new PrometheusExporter();
+
+const sdk = new NodeSDK({
+  // traceExporter: ...,
+  metricReader: prometheus,
+  instrumentations: [getNodeAutoInstrumentations()],
+});
+
+sdk.start();