[Backport 2.14] [DOC] Add pipeline processor documentation

_ingest-pipelines/processors/pipeline.md

@@ -0,0 +1,183 @@
+---
+layout: default
+title: Pipeline
+parent: Ingest processors
+nav_order: 200
+---
+
+# Pipeline processor
+
+The `pipeline` processor allows a pipeline to reference and include another predefined pipeline. This can be useful when you have a set of common processors that need to be shared across multiple pipelines. Instead of redefining those common processors in each pipeline, you can create a separate base pipeline containing the shared processors and then reference that base pipeline from other pipelines using the pipeline processor.
+
+The following is the syntax for the `pipeline` processor:
+
+```json
+{
+  "pipeline": {
+    "name": "general-pipeline"
+  }
+}
+```
+{% include copy-curl.html %}
+
+## Configuration parameters
+
+The following table lists the required and optional parameters for the `pipeline` processor.
+
+Parameter | Required/Optional | Description |
+|-----------|-----------|-----------|
+`name` | Required	| The name of the pipeline to execute.
+`description` | Optional | A description of the processor's purpose or configuration.
+`if` | Optional | Specifies to conditionally execute the processor.
+`ignore_failure` | Optional | Specifies to ignore processor failures. See [Handling pipeline failures]({{site.url}}{{site.baseurl}}/ingest-pipelines/pipeline-failures/).
+`on_failure` | Optional | Specifies to handle processor failures. See [Handling pipeline failures]({{site.url}}{{site.baseurl}}/ingest-pipelines/pipeline-failures/).
+`tag` | Optional | An 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 general pipeline named `general-pipeline` and then creates a new pipeline named `outer-pipeline`, which references the `general-pipeline`: 
+
+```json
+PUT _ingest/pipeline/general_pipeline  
+{  
+  "description": "a general pipeline",  
+  "processors": [  
+    {  
+      "uppercase": {  
+        "field": "protocol"  
+      },  
+      "remove": {  
+        "field": "name"  
+      }  
+    }  
+  ]  
+}
+```
+{% include copy-curl.html %}
+
+```json
+PUT _ingest/pipeline/outer-pipeline  
+{  
+  "description": "an outer pipeline referencing the general pipeline",  
+  "processors": [  
+    {  
+      "pipeline": {  
+        "name": "general-pipeline"  
+      }  
+    }  
+  ]  
+}
+```
+{% 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/outer-pipeline/_simulate
+{  
+  "docs": [  
+    {  
+      "_source": {  
+        "protocol": "https",  
+        "name":"test"  
+      }  
+    }  
+  ]  
+}  
+```
+{% 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": {  
+          "protocol": "HTTPS"  
+        },  
+        "_ingest": {  
+          "timestamp": "2024-05-24T02:43:43.700735801Z"  
+        }  
+      }  
+    }  
+  ]  
+}
+```
+{% 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=outer-pipeline  
+{  
+  "protocol": "https",  
+  "name": "test"  
+}  
+```
+{% include copy-curl.html %}
+
+#### Response
+
+The request indexes the document with the `protocol` field converted to uppercase and the field name removed from the index `testindex1`, as shown in the following response:
+
+```json
+{  
+  "_index": "testindex1",  
+  "_id": "1",  
+  "_version": 2,  
+  "result": "created",  
+  "_shards": {  
+    "total": 2,  
+    "successful": 2,  
+    "failed": 0  
+  },  
+  "_seq_no": 1,  
+  "_primary_term": 1  
+}  
+```
+{% 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 %}
+
+#### Response
+
+The response shows the document with the `protocol` field converted to uppercase and the field name removed:
+
+```json
+{  
+  "_index": "testindex1",  
+  "_id": "1",  
+  "_version": 2,  
+  "_seq_no": 1,  
+  "_primary_term": 1,  
+  "found": true,  
+  "_source": {  
+    "protocol": "HTTPS"  
+  }  
+}  
+```
+