[Backport 2.14] [DOC] Add set processor documentation

_ingest-pipelines/processors/set.md

@@ -0,0 +1,155 @@
+---
+layout: default
+title: Set
+parent: Ingest processors
+nav_order: 240
+---
+
+# Set processor
+
+The `set` processor adds or updates fields in a document. It sets one field and associates it with the specified value. If the field already exists, then its value is replaced with the provided one unless the `override` parameter is set to `false`. When `override` is `false` and the specified field exists, the value of the field remains unchanged.
+
+The following is the syntax for the `set` processor:
+
+```json
+{
+  "description": "...",
+  "processors": [
+    {
+      "set": {
+        "field": "new_field",
+        "value": "some_value"
+      }
+    }
+  ]
+}
+```
+{% include copy-curl.html %}
+
+## Configuration parameters
+
+The following table lists the required and optional parameters for the `set` processor.
+
+Parameter | Required/Optional | Description |
+|-----------|-----------|-----------|
+`field` | Required | The name of the field to be set or updated. Supports [template snippets]({{site.url}}{{site.baseurl}}/ingest-pipelines/create-ingest/#template-snippets).
+`value` | Required | The value assigned to the field. Supports [template snippets]({{site.url}}{{site.baseurl}}/ingest-pipelines/create-ingest/#template-snippets).
+`override` | Optional | A Boolean flag that determines whether the processor should override the existing value of the field.
+`ignore_empty_value` | Optional | A Boolean flag that determines whether the processor should ignore `null` values or empty strings. Default is `false`.
+`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 a list of processors to run if the processor fails during execution. These processors are executed in the order they are specified.
+`tag` | Optional | An identifier tag for the processor. Useful for debugging in order to distinguish between processors of the same type.
+
+## 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 `set-pipeline` that uses the `set` processor to add a new field `new_field` with the value `some_value` to the document: 
+
+```json
+PUT _ingest/pipeline/set-pipeline
+{
+  "description": "Adds a new field 'new_field' with the value 'some_value'",
+  "processors": [
+    {
+      "set": {
+        "field": "new_field",
+        "value": "some_value"
+      }
+    }
+  ]
+}
+```
+{% 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/set-pipeline/_simulate
+{
+  "docs": [
+    {
+      "_source": {
+        "existing_field": "value"
+      }
+    }
+  ]
+}
+```
+{% 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": {
+          "existing_field": "value",
+          "new_field": "some_value"
+        },
+        "_ingest": {
+          "timestamp": "2024-05-30T21:56:15.066180712Z"
+        }
+      }
+    }
+  ]
+}
+```
+{% include copy-curl.html %}
+
+### Step 3: Ingest a document 
+
+The following query ingests a document into an index named `testindex1`:
+
+```json
+POST testindex1/_doc?pipeline=set-pipeline
+{
+  "existing_field": "value"
+}
+```
+{% include copy-curl.html %}
+
+#### Response
+
+The request indexes the document into the index `testindex1` and then indexes all documents with the `new_field` set to `some_value`, as shown in the following response:
+
+```json
+{
+  "_index": "testindex1",
+  "_id": "1",
+  "_version": 1,
+  "result": "created",
+  "_shards": {
+    "total": 2,
+    "successful": 1,
+    "failed": 0
+  },
+  "_seq_no": 0,
+  "_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 %}