Add missing Fleet page (#627)

Author: colleenmcginnis

reference/ingestion-tools/fleet/otel-agent-transform.md

@@ -0,0 +1,93 @@
+---
+mapped_pages:
+  - https://www.elastic.co/guide/en/fleet/master/otel-agent-transform.html
+---
+
+# Transform an installed {{agent}} to run as an OTel Collector [otel-agent-transform]
+
+::::{warning}
+This functionality is in technical preview and may be changed or removed in a future release. Elastic will work to fix any issues, but features in technical preview are not subject to the support SLA of official GA features.
+::::
+
+
+If you have a currently installed standalone {{agent}}, it can be configured to run as an [OTel Collector](otel-agent.md). This allows you to run {{agent}} both as a service and in an OTel Collector mode.
+
+In order to configure an installed standalone {{agent}} to run as an OTel Collector, it’s enough to include a valid [OTel Collector](otel-agent.md) configuration in the `elastic-agent.yml` file, as shown in the following example.
+
+## Example: configure {{agent}} to ingest host logs and metrics into Elasticsearch using the OTel Collector [_example_configure_agent_to_ingest_host_logs_and_metrics_into_elasticsearch_using_the_otel_collector]
+
+**Prerequisites**
+
+You’ll need the following:
+
+1. A suitable [{{es}} API key](grant-access-to-elasticsearch.md#create-api-key-standalone-agent) for authenticating on Elasticsearch
+2. An installed standalone {agent}
+3. A valid OTel Collector configuration. In this example we’ll use the OTel sample configuration included in the {{agent}} repository: `otel_samples/platformlogs_hostmetrics.yml`.
+
+    * [Linux version](https://github.com/elastic/elastic-agent/blob/main/internal/pkg/otel/samples/linux/platformlogs_hostmetrics.yml)
+    * [MacOS version](https://github.com/elastic/elastic-agent/blob/main/internal/pkg/otel/samples/darwin/platformlogs_hostmetrics.yml)
+
+
+**Steps**
+
+To change a running standalone {{agent}} to run as an OTel Collector:
+
+1. Create a directory where the OTel Collector can save its state. In this example we use `<{{agent}} install directory>/data/otelcol`.
+2. Open the `<{{agent}} install directory>/otel_samples/platformlogs_hostmetrics.yml` file for editing.
+3. Set environment details to be used by OTel Collector:
+
+    * **Option 1:** Define environment variables for the {{agent}} service:
+
+        * `ELASTIC_ENDPOINT`: The URL of the {{es}} instance where data will be sent
+        * `ELASTIC_API_KEY`: The API Key to use to authenticate with {es}
+        * `STORAGE_DIR`: The directory where the OTel Collector can persist its state
+
+    * **Option 2:** Replace the environment variable references in the sample configuration with the corresponding values:
+
+        * `${env:ELASTIC_ENDPOINT}`:The URL of the {{es}} instance where data will be sent
+        * `${env:ELASTIC_API_KEY}`: The API Key to use to authenticate with {es}
+        * `${env:STORAGE_DIR}`: The directory where the OTel Collector can persist its state
+
+4. Save the opened OTel configuration as `elastic-agent.yml`, overwriting the default configuration of the installed agent.
+5. Run the `elastic-agent status` command to verify that the new configuration has been correctly applied:
+
+    ```shell
+    elastic-agent status
+    ```
+
+    The OTel Collector running configuration should appear under `elastic-agent` key (note the `extensions` and `pipeline` keys):
+
+    ```shell
+    ┌─ fleet
+    │  └─ status: (STOPPED) Not enrolled into Fleet
+    └─ elastic-agent
+       ├─ status: (HEALTHY) Running
+       ├─ extensions
+       │  ├─ status: StatusOK
+       │  └─ extension:file_storage
+       │     └─ status: StatusOK
+       ├─ pipeline:logs/platformlogs
+       │  ├─ status: StatusOK
+       │  ├─ exporter:elasticsearch/otel
+       │  │  └─ status: StatusOK
+       │  ├─ processor:resourcedetection
+       │  │  └─ status: StatusOK
+       │  └─ receiver:filelog/platformlogs
+       │     └─ status: StatusOK
+       └─ pipeline:metrics/hostmetrics
+          ├─ status: StatusOK
+          ├─ exporter:elasticsearch/ecs
+          │  └─ status: StatusOK
+          ├─ processor:attributes/dataset
+          │  └─ status: StatusOK
+          ├─ processor:elasticinframetrics
+          │  └─ status: StatusOK
+          ├─ processor:resource/process
+          │  └─ status: StatusOK
+          ├─ processor:resourcedetection
+          │  └─ status: StatusOK
+          └─ receiver:hostmetrics/system
+             └─ status: StatusOK
+    ```
+
+6. Congratulations! Host logs and metrics are now being collected and ingested by the {{agent}} service running an OTel Collector instance. For further details about OpenTelemetry collector components supported by {{agent}}, refer to the [Elastic Distribution for OpenTelemetry Collector README](https://github.com/elastic/elastic-agent/tree/main/internal/pkg/otel#components).

reference/toc.yml

@@ -63,6 +63,7 @@ toc:
                   - file: ingestion-tools/fleet/ingest-pipeline-kubernetes.md
                   - file: ingestion-tools/fleet/agent-environment-variables.md
               - file: ingestion-tools/fleet/otel-agent.md
+              - file: ingestion-tools/fleet/otel-agent-transform.md
               - file: ingestion-tools/fleet/elastic-agent-unprivileged.md
               - file: ingestion-tools/fleet/install-agent-msi.md
               - file: ingestion-tools/fleet/installation-layout.md