Add index mode to get data stream API (#122486)

This commit adds the `index_mode` for both the data stream and each
backing index to the output of `GET /_data_stream`. An example looks
like:

```
{
  "data_streams" : [
    {
      "name" : "foo-things",
      "indices" : [
        {
          "index_name" : ".ds-foo-things-2025.02.13-000001",
          ...
          "index_mode" : "standard"
        }
      ],
      ...
      "index_mode" : "standard"
    },
    {
      "name" : "logs-foo-bar",
      "indices" : [
        {
          "index_name" : ".ds-logs-foo-bar-2025.02.13-000001",
          ...
          "index_mode" : "logsdb"
        },
        {
          "index_name" : ".ds-logs-foo-bar-2025.02.13-000002",
          ...
          "index_mode" : "logsdb"
        }
      ],
      ...
      "index_mode" : "logsdb",
    }
  ]
}
```

Author: dakrone

docs/changelog/122486.yaml

@@ -0,0 +1,5 @@
+pr: 122486
+summary: Add index mode to get data stream API
+area: Data streams
+type: enhancement
+issues: []

docs/reference/indices/get-data-stream.asciidoc

@@ -0,0 +1,376 @@
+[role="xpack"]
+[[indices-get-data-stream]]
+=== Get data stream API
+++++
+<titleabbrev>Get data stream</titleabbrev>
+++++
+
+.New API reference
+[sidebar]
+--
+For the most up-to-date API details, refer to {api-es}/group/endpoint-data-stream[Data stream APIs].
+--
+
+Retrieves information about one or more <<data-streams,data streams>>.
+See <<get-info-about-data-stream>>.
+
+////
+[source,console]
+----
+PUT /_ilm/policy/my-lifecycle-policy
+{
+  "policy": {
+    "phases": {
+      "hot": {
+        "actions": {
+          "rollover": {
+            "max_primary_shard_size": "25GB"
+          }
+        }
+      },
+      "delete": {
+        "min_age": "30d",
+        "actions": {
+          "delete": {}
+        }
+      }
+    }
+  }
+}
+
+PUT /_index_template/my-index-template
+{
+  "index_patterns": [ "my-data-stream*" ],
+  "data_stream": {},
+  "template": {
+    "settings": {
+      "index.lifecycle.name": "my-lifecycle-policy"
+    }
+  },
+  "_meta": {
+    "my-meta-field": "foo"
+  }
+}
+
+PUT /_data_stream/my-data-stream
+
+POST /my-data-stream/_rollover
+
+PUT /_data_stream/my-data-stream-two
+
+DELETE /_data_stream/my-data-stream*/_lifecycle
+----
+// TESTSETUP
+////
+
+////
+[source,console]
+----
+DELETE /_data_stream/*
+DELETE /_index_template/*
+DELETE /_ilm/policy/my-lifecycle-policy
+----
+// TEARDOWN
+////
+
+[source,console]
+----
+GET /_data_stream/my-data-stream
+----
+
+[[get-data-stream-api-request]]
+==== {api-request-title}
+
+`GET /_data_stream/<data-stream>`
+
+[[get-data-stream-api-prereqs]]
+==== {api-prereq-title}
+
+* If the {es} {security-features} are enabled, you must have the
+`view_index_metadata` or `manage` <<privileges-list-indices,index privilege>>
+for the data stream.
+
+[[get-data-stream-api-path-params]]
+==== {api-path-parms-title}
+
+`<data-stream>`::
+(Optional, string)
+Comma-separated list of data stream names used to limit the request. Wildcard
+(`*`) expressions are supported. If omitted, all data streams will be
+returned.
+
+[role="child_attributes"]
+[[get-data-stream-api-query-parms]]
+==== {api-query-parms-title}
+
+include::{es-ref-dir}/rest-api/common-parms.asciidoc[tag=ds-expand-wildcards]
++
+Defaults to `open`.
+
+`include_defaults`::
+(Optional, Boolean) Functionality in preview:[]. If `true`, return all default settings in the response.
+Defaults to `false`.
+
+`verbose`::
+(Optional, Boolean). If `true`, Returns the `maximum_timestamp` corresponding to the `@timestamp` field for documents in the data stream.
+Defaults to `false`.
+
+[role="child_attributes"]
+[[get-data-stream-api-response-body]]
+==== {api-response-body-title}
+
+`data_streams`::
+(array of objects)
+Contains information about retrieved data streams.
++
+.Properties of objects in `data_streams`
+[%collapsible%open]
+====
+`name`::
+(string)
+Name of the data stream.
+
+`timestamp_field`::
+(object)
+Contains information about the data stream's `@timestamp` field.
++
+.Properties of `timestamp_field`
+[%collapsible%open]
+=====
+`name`::
+(string)
+Name of the data stream's timestamp field, which must be `@timestamp`. The
+`@timestamp` field must be included in every document indexed to the data
+stream.
+=====
+
+`indices`::
+(array of objects)
+Array of objects containing information about the data stream's backing
+indices.
++
+The last item in this array contains information about the stream's current
+<<data-stream-write-index,write index>>.
++
+.Properties of `indices` objects
+[%collapsible%open]
+=====
+`index_name`::
+(string)
+Name of the backing index. For naming conventions, see
+<<data-streams-generation>>.
+
+`index_uuid`::
+(string)
+Universally unique identifier (UUID) for the index.
+
+`prefer_ilm`::
+(boolean)
+Functionality in preview:[]. Indicates if this index is configured to prefer {ilm}
+when both {ilm-cap} and <<data-stream-lifecycle, Data stream lifecycle>> are configured to
+manage this index.
+
+`managed_by`::
+(string)
+Functionality in preview:[]. Indicates the system that managed this index.
+=====
+
+`generation`::
+(integer)
+Current <<data-streams-generation,generation>> for the data stream. This number
+acts as a cumulative count of the stream's rollovers, starting at `1`.
+
+`_meta`::
+(object)
+Custom metadata for the stream, copied from the `_meta` object of the
+stream's matching <<create-index-template,index template>>. If empty,
+the response omits this property.
+
+`status`::
+(string)
+<<cluster-health,Health status>> of the data stream.
++
+This health status is based on the state of the primary and replica shards of
+the stream's backing indices.
++
+.Values for `status`
+[%collapsible%open]
+=====
+`GREEN`:::
+All shards are assigned.
+
+`YELLOW`:::
+All primary shards are assigned, but one or more replica shards are
+unassigned.
+
+`RED`:::
+One or more primary shards are unassigned, so some data is unavailable.
+=====
+
+`template`::
+(string)
+Name of the index template used to create the data stream's backing indices.
++
+The template's index pattern must match the name of this data stream. See
+<<create-index-template,create an index template>>.
+
+`ilm_policy`::
+(string)
+Name of the current {ilm-init} lifecycle policy in the stream's matching index
+template. This lifecycle policy is set in the `index.lifecycle.name` setting.
++
+If the template does not include a lifecycle policy, this property is not
+included in the response.
++
+NOTE: A data stream's backing indices may be assigned different lifecycle
+policies. To retrieve the lifecycle policy for individual backing indices,
+use the <<indices-get-settings,get index settings API>>.
+
+`next_generation_managed_by`::
+(string)
+Functionality in preview:[]. Indicates the system that will managed the next generation index
+(i.e. the next data stream write index).
+
+`prefer_ilm`::
+(boolean)
+Functionality in preview:[]. Indicates if the index template used to create the data
+stream's backing indices is configured to prefer {ilm-cap} when both {ilm-cap} and
+<<data-stream-lifecycle, Data stream lifecycle>> are configured to manage this index.
+
+`hidden`::
+(Boolean) If `true`, the data stream is <<multi-hidden,hidden>>.
+
+`system`::
+(Boolean)
+If `true`, the data stream is created and managed by an Elastic stack component
+and cannot be modified through normal user interaction.
+
+`allow_custom_routing`::
+(Boolean)
+If `true`, the data stream this data stream allows custom routing on write request.
+
+`replicated`::
+(Boolean)
+If `true`, the data stream is created and managed by {ccr} and the local
+cluster can not write into this data stream or change its mappings.
+
+`lifecycle`::
+(object)
+Functionality in preview:[]. Contains the configuration for the data stream lifecycle management of this data stream.
++
+.Properties of `lifecycle`
+[%collapsible%open]
+=====
+`data_retention`::
+(string)
+If defined, every document added to this data stream will be stored at least for this time frame. Any time after this
+duration the document could be deleted. When empty, every document in this data stream will be stored indefinitely.
+
+`rollover`::
+(object)
+The conditions which will trigger the rollover of a backing index as configured by the cluster setting
+`cluster.lifecycle.default.rollover`. This property is an implementation detail and it will only be retrieved when the query
+param `include_defaults` is set to `true`. The contents of this field are subject to change.
+=====
+
+`rollover_on_write`::
+(Boolean)
+If `true`, the next write to this data stream will trigger a rollover first and the document will be
+indexed in the new backing index. If the rollover fails the indexing request will fail too.
+====
+
+[[get-data-stream-api-example]]
+==== {api-examples-title}
+
+[source,console]
+----
+GET _data_stream/my-data-stream*
+----
+
+The API returns the following response:
+
+[source,console-result]
+----
+{
+  "data_streams": [
+    {
+      "name": "my-data-stream",
+      "timestamp_field": {
+        "name": "@timestamp"
+      },
+      "indices": [
+        {
+          "index_name": ".ds-my-data-stream-2099.03.07-000001",
+          "index_uuid": "xCEhwsp8Tey0-FLNFYVwSg",
+          "prefer_ilm": true,
+          "ilm_policy": "my-lifecycle-policy",
+          "managed_by": "Index Lifecycle Management",
+          "index_mode": "standard"
+        },
+        {
+          "index_name": ".ds-my-data-stream-2099.03.08-000002",
+          "index_uuid": "PA_JquKGSiKcAKBA8DJ5gw",
+          "prefer_ilm": true,
+          "ilm_policy": "my-lifecycle-policy",
+          "managed_by": "Index Lifecycle Management",
+          "index_mode": "standard"
+        }
+      ],
+      "generation": 2,
+      "_meta": {
+        "my-meta-field": "foo"
+      },
+      "status": "GREEN",
+      "index_mode": "standard",
+      "next_generation_managed_by": "Index Lifecycle Management",
+      "prefer_ilm": true,
+      "template": "my-index-template",
+      "ilm_policy": "my-lifecycle-policy",
+      "hidden": false,
+      "system": false,
+      "allow_custom_routing": false,
+      "replicated": false,
+      "rollover_on_write": false
+    },
+    {
+      "name": "my-data-stream-two",
+      "timestamp_field": {
+        "name": "@timestamp"
+      },
+      "indices": [
+        {
+          "index_name": ".ds-my-data-stream-two-2099.03.08-000001",
+          "index_uuid": "3liBu2SYS5axasRt6fUIpA",
+          "prefer_ilm": true,
+          "ilm_policy": "my-lifecycle-policy",
+          "managed_by": "Index Lifecycle Management",
+          "index_mode": "standard"
+        }
+      ],
+      "generation": 1,
+      "_meta": {
+        "my-meta-field": "foo"
+      },
+      "status": "YELLOW",
+      "index_mode": "standard",
+      "next_generation_managed_by": "Index Lifecycle Management",
+      "prefer_ilm": true,
+      "template": "my-index-template",
+      "ilm_policy": "my-lifecycle-policy",
+      "hidden": false,
+      "system": false,
+      "allow_custom_routing": false,
+      "replicated": false,
+      "rollover_on_write": false
+    }
+  ]
+}
+----
+// TESTRESPONSE[s/"index_name": ".ds-my-data-stream-2099.03.07-000001"/"index_name": $body.data_streams.0.indices.0.index_name/]
+// TESTRESPONSE[s/"index_uuid": "xCEhwsp8Tey0-FLNFYVwSg"/"index_uuid": $body.data_streams.0.indices.0.index_uuid/]
+// TESTRESPONSE[s/"index_name": ".ds-my-data-stream-2099.03.08-000002"/"index_name": $body.data_streams.0.indices.1.index_name/]
+// TESTRESPONSE[s/"index_uuid": "PA_JquKGSiKcAKBA8DJ5gw"/"index_uuid": $body.data_streams.0.indices.1.index_uuid/]
+// TESTRESPONSE[s/"index_name": ".ds-my-data-stream-two-2099.03.08-000001"/"index_name": $body.data_streams.1.indices.0.index_name/]
+// TESTRESPONSE[s/"index_uuid": "3liBu2SYS5axasRt6fUIpA"/"index_uuid": $body.data_streams.1.indices.0.index_uuid/]
+// TESTRESPONSE[s/"status": "GREEN"/"status": "YELLOW"/]
+// TESTRESPONSE[s/"replicated": false/"replicated": false,"failure_store":{"enabled": false, "indices": [], "rollover_on_write": true}/]