[DOC] Add join processor documentation

_ingest-pipelines/processors/join.md

@@ -0,0 +1,135 @@
+---
+layout: default
+title: Join
+parent: Ingest processors
+nav_order: 160
+---
+
+# Join processor
+
+The `join` processor concatenates the elements of an array into a single string value, using a specified separator between each element. It throws an exception if the provided input is not an array.
+
+The following is the syntax for the `join` processor:
+
+```json
+{
+  "join": {
+    "field": "field_name",
+    "separator": "separator_string"
+  }
+}
+```
+{% include copy-curl.html %}
+
+## Configuration parameters
+
+The following table lists the required and optional parameters for the `join` processor.
+
+Parameter | Required/Optional | Description |
+|-----------|-----------|-----------|
+`field` | Required | The field name where the join operator is applied. Must be an array.
+`separator` | Required | A string separator to use when joining field values. If not specified, the values are concatenated without a separator.
+`target_field` | Optional | The field to assign the cleaned value to. If not specified, field is updated in-place.
+`description` | Optional | Description of the processor's purpose or configuration.
+`if` | Optional | Conditionally execute the processor.
+`ignore_failure` | Optional | Ignore failures for the processor. See [Handling pipeline failures]({{site.url}}{{site.baseurl}}/ingest-pipelines/pipeline-failures/).
+`on_failure` | Optional | Handle failures for the processor. See [Handling pipeline failures]({{site.url}}{{site.baseurl}}/ingest-pipelines/pipeline-failures/).
+`tag` | Optional | Identifier for the processor. Useful for debugging and metrics.
+
+## Using the processor
+
+Follow these steps to use the processor in a pipeline.
+
+### Step 1: Create a pipeline
+
+The following query creates a pipeline named `example-join-pipeline` that uses the `join` processor to concatenate all the values of the `uri`  field, separating them with the specified separator `/`: 
+
+```json
+PUT _ingest/pipeline/example-join-pipeline  
+{  
+  "description": "Example pipeline using the join processor",  
+  "processors": [  
+    {  
+      "join": {  
+        "field": "uri",  
+        "separator": "/"  
+      }  
+    }  
+  ]  
+}  
+```
+{% include copy-curl.html %}
+
+### Step 2 (Optional): Test the pipeline
+
+It is recommended that you test your pipeline before you ingest documents.
+{: .tip}
+
+To test the pipeline, run the following query:
+
+```json
+POST _ingest/pipeline/example-join-pipeline/_simulate  
+{  
+  "docs": [  
+    {  
+      "_source": {  
+        "uri": [  
+          "app",  
+          "home",  
+          "overview"  
+        ]  
+      }  
+    }  
+  ]  
+}
+```
+{% include copy-curl.html %}
+
+#### Response
+
+The following example response confirms that the pipeline is working as expected:
+
+```json
+{  
+  "docs": [  
+    {  
+      "doc": {  
+        "_index": "_index",  
+        "_id": "_id",  
+        "_source": {  
+          "uri": "app/home/overview"  
+        },  
+        "_ingest": {  
+          "timestamp": "2024-05-24T02:16:01.00659117Z"  
+        }  
+      }  
+    }  
+  ]  
+}  
+```
+{% include copy-curl.html %}
+
+### Step 3: Ingest a document 
+
+The following query ingests a document into an index named `testindex1`:
+
+```json
+POST testindex1/_doc/1?pipeline=example-join-pipeline  
+{  
+  "uri": [  
+    "app",  
+    "home",  
+    "overview"  
+  ]  
+} 
+```
+{% include copy-curl.html %}
+
+### Step 4 (Optional): Retrieve the document
+
+To retrieve the document, run the following query:
+
+```json
+GET testindex1/_doc/1
+```
+{% include copy-curl.html %}