Add docs for open telemetry collector (#6429)

Signed-off-by: SungJin1212 <[email protected]>

Author: SungJin1212

docs/guides/open-telemetry-collector.md

@@ -0,0 +1,134 @@
+---
+title: "OpenTelemetry Collector"
+linkTitle: "OpenTelemetry Collector"
+weight: 10
+slug: opentelemetry-collector
+---
+
+This guide explains how to configure open-telemetry collector and OTLP(OpenTelemetry Protocol) configurations in the
+Cortex.
+
+## Context
+
+The [open-telemetry collector](https://opentelemetry.io/docs/collector/) can write collected metrics to the Cortex with
+the Prometheus and OTLP formats.
+
+## Push with Prometheus format
+
+To push metrics via the `Prometheus` format, we can
+use [prometheusremotewrite](https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/exporter/prometheusremotewriteexporter)
+exporter in the open-telemetry collector.
+In the `exporters` and `service` sections in the open-telemetry collector yaml file, we can add as follows:
+
+```
+exporters:
+  prometheusremotewrite:
+    endpoint: http://<cortex-endpoint>/api/v1/push
+    headers:
+      X-Scope-OrgId: <orgId>
+
+...
+
+service:
+  pipelines:
+    metrics:
+      receivers: [...]
+      processors: [...]
+      exporters: [prometheusremotewrite]
+```
+
+Please refer to [Authentication and Authorisation](./authentication-and-authorisation.md) section for the
+`X-Scope-OrgId` explanation.
+
+## Push with OTLP format
+
+To push metrics via the `OTLP` format, we can
+use [otlphttp](https://github.com/open-telemetry/opentelemetry-collector/tree/main/exporter/otlphttpexporter) exporter
+in the open-telemetry collector.
+In the `exporters` and `service` sections in the open-telemetry collector yaml file, we can add as follows:
+
+```
+exporters:
+  otlphttp:
+    endpoint: http://<cortex-endpoint>/api/v1/otlp
+    headers:
+      X-Scope-OrgId: <orgId>
+
+...
+
+service:
+  pipelines:
+    metrics:
+      receivers: [...]
+      processors: [...]
+      exporters: [otlphttp]
+```
+
+## Configure OTLP
+
+### target_info metric
+
+By default,
+the [target_info](https://github.com/prometheus/OpenMetrics/blob/main/specification/OpenMetrics.md#supporting-target-metadata-in-both-push-based-and-pull-based-systems)
+is enabled to write and can be disabled via `-distributor.otlp.disable-target-info=true`.
+
+### Resource attributes conversion
+
+The conversion of
+all [resource attributes](https://opentelemetry.io/docs/specs/semconv/resource/) to labels is
+disabled by default and can be enabled via
+`-distributor.otlp.convert-all-attributes=true`.
+
+You can specify the attributes converted to labels via `-distributor.promote-resource-attributes` flag. It is supported
+only if `-distributor.otlp.convert-all-attributes=false`.
+
+These flags can be configured via yaml:
+
+```
+limits:
+ promote_resource_attributes: <list of string>
+...
+distributor:
+  otlp:
+    convert_all_attributes: <boolean>
+    disable_target_info: <boolean>
+```
+
+These are the yaml examples:
+
+- Example 1: All of the resource attributes are converted, and the `target_info` metric is disabled to push.
+
+```
+distributor:
+  otlp:
+    convert_all_attributes: true
+    disable_target_info: true
+```
+
+- Example 2: Only `service.name` and `service.instance.id` resource attributes are converted to labels and the
+  `target_info` metric is enabled to push.
+
+```
+limits:
+ promote_resource_attributes: ["service.name", "service.instance.id"]
+distributor:
+  otlp:
+    convert_all_attributes: false
+    disable_target_info: false
+```
+
+### Configure promote resource attributes per tenants
+
+The `promote_resource_attributes` is a [runtime config](./overrides-exporter.md) so you can configure it per tenant.
+
+For example, this yaml file specifies `attr1` being converted to label in both `user-1` and `user-2`. But, the `attr2`
+is converted only for `user-2`.
+
+```
+overrides:
+  user-1:
+    promote_resource_attributes: ["attr1"]
+  user-2:
+    promote_resource_attributes: ["attr1", "attr2"]
+`
+```