Unify internal observability documentation - 1 of 3 (#4246)

Author: tiffany76

content/en/docs/collector/internal-telemetry.md

@@ -0,0 +1,115 @@
+---
+title: Internal telemetry
+weight: 25
+cSpell:ignore: journalctl kube otecol pprof tracez zpages
+---
+
+You can monitor the health of any OpenTelemetry Collector instance by checking
+its own internal telemetry. Read on to learn how to configure this telemetry to
+help you [troubleshoot](/docs/collector/troubleshooting/) Collector issues.
+
+## Activate internal telemetry in the Collector
+
+By default, the Collector exposes its own telemetry in two ways:
+
+- Internal [metrics](#configure-internal-metrics) are exposed using a Prometheus
+  interface which defaults to port `8888`.
+- [Logs](#configure-internal-logs) are emitted to `stderr` by default.
+
+### Configure internal metrics
+
+You can configure how internal metrics are generated and exposed by the
+Collector. By default, the Collector generates basic metrics about itself and
+exposes them for scraping at `http://127.0.0.1:8888/metrics`. You can expose the
+endpoint to one specific or all network interfaces when needed. For
+containerized environments, you might want to expose this port on a public
+interface.
+
+Set the address in the config `service::telemetry::metrics`:
+
+```yaml
+service:
+  telemetry:
+    metrics:
+      address: '0.0.0.0:8888'
+```
+
+You can enhance the metrics telemetry level using the `level` field. The
+following is a list of all possible values and their explanations.
+
+- `none` indicates that no telemetry data should be collected.
+- `basic` is the recommended value and covers the basics of the service
+  telemetry.
+- `normal` adds other indicators on top of basic.
+- `detailed` adds dimensions and views to the previous levels.
+
+For example:
+
+```yaml
+service:
+  telemetry:
+    metrics:
+      level: detailed
+      address: ':8888'
+```
+
+The Collector can also be configured to scrape its own metrics and send them
+through configured pipelines. For example:
+
+```yaml
+receivers:
+  prometheus:
+    config:
+      scrape_configs:
+        - job_name: 'otelcol'
+          scrape_interval: 10s
+          static_configs:
+            - targets: ['0.0.0.0:8888']
+          metric_relabel_configs:
+            - source_labels: [__name__]
+              regex: '.*grpc_io.*'
+              action: drop
+exporters:
+  debug:
+service:
+  pipelines:
+    metrics:
+      receivers: [prometheus]
+      exporters: [debug]
+```
+
+{{% alert title="Caution" color="warning" %}}
+
+Self-monitoring is a risky practice. If an issue arises, the source of the
+problem is unclear and the telemetry is unreliable.
+
+{{% /alert %}}
+
+### Configure internal logs
+
+You can find log output in `stderr`. The verbosity level for logs defaults to
+`INFO`, but you can adjust it in the config `service::telemetry::logs`:
+
+```yaml
+service:
+  telemetry:
+    logs:
+      level: 'debug'
+```
+
+You can also see logs for the Collector on a Linux systemd system using
+`journalctl`:
+
+{{< tabpane text=true >}} {{% tab "All logs" %}}
+
+```sh
+journalctl | grep otelcol
+```
+
+{{% /tab %}} {{% tab "Errors only" %}}
+
+```sh
+journalctl | grep otelcol | grep Error
+```
+
+{{% /tab %}} {{< /tabpane >}}

content/en/docs/collector/troubleshooting.md

@@ -8,6 +8,12 @@ This page describes some options when troubleshooting the health or performance
 of the OpenTelemetry Collector. The Collector provides a variety of metrics,
 logs, and extensions for debugging issues.
 
+## Internal telemetry
+
+You can configure and use the Collector's own
+[internal telemetry](/docs/collector/internal-telemetry/) to monitor its
+performance.
+
 ## Sending test data
 
 For certain types of issues, particularly verifying configuration and debugging

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