[FSTORE-1780] onlinefs observability docs (#491)

Author: bubriks

docs/assets/images/guides/feature_group/online_ingestion.png

@@ -0,0 +1,101 @@
+---
+description: Documentation on Online ingestion observability in Hopsworks.
+---
+
+# Online ingestion observability
+
+## Introduction
+
+Knowing when ingested data becomes available for online serving—and understanding the cause of any ingestion failures—is crucial for users. To address this, the Hopsworks API provides observability features for online ingestion, allowing you to monitor ingestion status and troubleshoot issues.
+
+This guide explains how to use these observability features for online feature groups in Hopsworks, with examples using both the HSFS APIs and the user interface.
+
+## Prerequisites
+
+Before you begin this guide we suggest you read the [Feature Group](../../../concepts/fs/feature_group/fg_overview.md) concept page to understand what a feature group is and how it fits in the ML pipeline.
+
+## Using the Hopsworks API
+
+### Create a Feature Group and Ingest Data
+
+First, create an online-enabled feature group and insert data into it:
+
+=== "Python"
+
+    ```python
+    fg = fs.create_feature_group(
+        name="feature_group_name",
+        version=feature_group_version,
+        primary_key=feature_group_primary_keys,
+        online_enabled=True
+    )
+
+    fg.insert(fg_df)
+    ```
+
+### Retrieve Online Ingestion Status
+
+After inserting data, you can monitor the ingestion progress:
+
+**Get the latest ingestion instance**
+
+=== "Python"
+
+    ```python
+    oi = fg.get_latest_online_ingestion()
+    ```
+
+**Get a specific ingestion by its ID**
+
+=== "Python"
+
+    ```python
+    oi = fg.get_online_ingestion(ingestion_id)
+    ```
+
+### Use the Online Ingestion Object
+
+The online ingestion object provides methods to track and debug the ingestion process:
+
+**Wait for completion**
+
+Wait for the online ingestion to finish (equivalent to `fg.insert(fg_df, wait=True)`):
+
+=== "Python"
+
+    ```python
+    oi.wait_for_completion()
+    ```
+
+**Print mini-batch results**
+
+Check the results of the ingestion. If the status is `UPSERTED` and the number of rows matches your data, the ingestion was successful:
+
+=== "Python"
+
+    ```python
+    print([result.to_dict() for result in oi.results])
+    # Example output: [{'onlineIngestionId': 1, 'status': 'UPSERTED', 'rows': 10}]
+    ```
+
+**Print ingestion service logs**
+
+Retrieve logs from the online ingestion service to diagnose any issues:
+
+=== "Python"
+
+    ```python
+    oi.print_logs(priority="error", size=5)
+    ```
+
+## Using the UI
+
+### Viewing Online Ingestion Status
+
+After inserting data into an online-enabled feature group, you can track the ingestion progress in the `Recent activities` section of the feature group in the Hopsworks UI.
+
+<p align="center">
+  <figure>
+    <img src="../../../../assets/images/guides/feature_group/online_ingestion.png" alt="See online ingestion status">
+  </figure>
+</p>

docs/user_guides/fs/feature_group/online_ingestion_observability.md

@@ -85,6 +85,7 @@ nav:
                   - Advanced guide: user_guides/fs/feature_monitoring/feature_monitoring_advanced.md
               - Notification: user_guides/fs/feature_group/notification.md
               - On-Demand Transformations: user_guides/fs/feature_group/on_demand_transformations.md
+              - Online Ingestion Observability: user_guides/fs/feature_group/online_ingestion_observability.md
           - Feature View:
               - user_guides/fs/feature_view/index.md
               - Overview: user_guides/fs/feature_view/overview.md