Add Rollover API (#7685)

* Add Rollover API.

Signed-off-by: Archer <naarcha@amazon.com>

* Apply suggestions from code review

Signed-off-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>

* Make rollover match template.

Signed-off-by: Archer <naarcha@amazon.com>

* Apply suggestions from code review

Co-authored-by: Melissa Vagi <vagimeli@amazon.com>
Signed-off-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>

* Update _api-reference/index-apis/rollover.md

Co-authored-by: Melissa Vagi <vagimeli@amazon.com>
Signed-off-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>

* Update _api-reference/index-apis/rollover.md

Co-authored-by: Melissa Vagi <vagimeli@amazon.com>
Signed-off-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: Nathan Bower <nbower@amazon.com>
Co-authored-by: Melissa Vagi <vagimeli@amazon.com>
Signed-off-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>

* Update _api-reference/index-apis/rollover.md

Co-authored-by: Nathan Bower <nbower@amazon.com>
Signed-off-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>

---------

Signed-off-by: Archer <naarcha@amazon.com>
Signed-off-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>
Co-authored-by: Melissa Vagi <vagimeli@amazon.com>
Co-authored-by: Nathan Bower <nbower@amazon.com>

_api-reference/index-apis/rollover.md

@@ -0,0 +1,195 @@
+---
+layout: default
+title: Rollover Index
+parent: Index APIs
+nav_order: 63
+---
+
+# Rollover Index
+Introduced 1.0
+{: .label .label-purple }
+
+The Rollover Index API creates a new index for a data stream or index alias based on the `wait_for_active_shards` setting.
+
+## Path and HTTP methods
+
+```json
+POST /<rollover-target>/_rollover/
+POST /<rollover-target>/_rollover/<target-index>
+```
+
+## Rollover types
+
+You can roll over a data stream, an index alias with one index, or an index alias with a write index.
+
+### Data stream
+
+When you perform a rollover operation on a data stream, the API generates a fresh write index for that stream. Simultaneously, the stream's preceding write index transforms into a regular backing index. Additionally, the rollover process increments the generation count of the data stream. Data stream rollovers do not support specifying index settings in the request body.
+
+### Index alias with one index
+
+When initiating a rollover on an index alias associated with a single index, the API generates a new index and disassociates the original index from the alias.
+
+### Index alias with a write index
+
+When an index alias references multiple indexes, one index must be designated as the write index. During a rollover, the API creates a new write index with its `is_write_index` property set to `true` while updating the previous write index by setting its `is_write_index property` to `false.`
+
+## Incrementing index names for an alias
+
+During the index alias rollover process, if you don't specify a custom name and the current index's name ends with a hyphen followed by a number (for example, `my-index-000001` or `my-index-3`), then the rollover operation will automatically increment that number for the new index's name. For instance, rolling over `my-index-000001` will generate `my-index-000002`. The numeric portion is always padded with leading zeros to ensure a consistent length of six characters.
+
+## Using date math with index rollovers
+
+When using an index alias for time-series data, you can leverage [date math](https://opensearch.org/docs/latest/field-types/supported-field-types/date/) in the index name to track the rollover date. For example, you can create an alias pointing to `my-index-{now/d}-000001`. If you create an alias on June 11, 2029, then the index name would be `my-index-2029.06.11-000001`. For a rollover on June 12, 2029, the new index would be named `my-index-2029.06.12-000002`. See [Roll over an index alias with a write index](#rolling-over-an-index-alias-with-a-write-index) for a practical example.
+
+## Path parameters
+
+The Rollover Index API supports the parameters listed in the following table.
+
+Parameter | Type | Description 
+:--- | :--- | :--- 
+`<rollover-target>` | String | The name of the data stream or index alias to roll over. Required. |
+`<target-index>` | String | The name of the index to create. Supports date math. Data streams do not support this parameter. If the name of the alias's current write index does not end with `-` and a number, such as `my-index-000001` or `my-index-2`, then the parameter is required. 
+
+## Query parameters
+
+The following table lists the supported query parameters.
+
+Parameter | Type | Description 
+:--- | :--- | :--- 
+`cluster_manager_timeout` | Time | The amount of time to wait for a connection to the cluster manager node. Default is `30s`.
+`timeout` | Time | The amount of time to wait for a response. Default is `30s`.
+`wait_for_active_shards` | String | The number of active shards that must be available before OpenSearch processes the request. Default is `1` (only the primary shard). You can also set to `all` or a positive integer. Values greater than `1` require replicas. For example, if you specify a value of `3`, then the index must have two replicas distributed across two additional nodes in order for the operation to succeed.
+
+## Request body
+
+The following request body parameters are supported.
+
+### `alias`
+
+The `alias` parameter specifies the alias name as the key. It is required when the `template` option exists in the request body. The object body contains the following optional parameters.
+
+
+Parameter | Type | Description
+:--- | :--- | :---
+`filter` | Query DSL object | The query that limits the number of documents that the alias can access.
+`index_routing` | String | The value that routes indexing operations to a specific shard. When specified, overwrites the `routing` value for indexing operations.
+`is_hidden` | Boolean | Hides or unhides the alias. When `true`, the alias is hidden. Default is `false`. Indexes for the alias must have matching values for this setting.
+`is_write_index` | Boolean | Specifies the write index. When `true`, the index is the write index for the alias. Default is `false`.
+`routing` | String | The value used to route index and search operations to a specific shard.
+`search_routing` | String | Routes search operations to a specific shard. When specified, it overwrites `routing` for search operations.
+
+### `mappings`
+
+The `mappings` parameter specifies the index field mappings. It is optional. See [Mappings and field types](https://opensearch.org/docs/latest/field-types/) for more information.
+
+### `conditions`
+
+The `conditions` parameter is an optional object defining criteria for triggering the rollover. When provided, OpenSearch only rolls over if the current index satisfies one or more specified conditions. If omitted, then the rollover occurs unconditionally without prerequisites.
+
+The object body supports the following parameters.
+
+Parameter | Type | Description 
+:--- | :--- | :--- 
+| `max_age` | Time units | Triggers a rollover after the maximum elapsed time since index creation is reached. The elapsed time is always calculated since the index creation time, even if the index origination date is configured to a custom date, such as when using the `index.lifecycle.parse_origination_date` or `index.lifecycle.origination_date` settings. Optional. |
+`max_docs` | Integer | Triggers a rollover after the specified maximum number of documents, excluding documents added since the last refresh and documents in replica shards. Optional. 
+`max_size` | Byte units  | Triggers a rollover when the index reaches a specified size, calculated as the total size of all primary shards. Replicas are not counted. Use the `_cat indices` API and check the `pri.store.size` value to see the current index size. Optional.
+`max_primary_shard_size` | Byte units  | Triggers a rollover when the largest primary shard in the index reaches a certain size. This is the maximum size of the primary shards in the index. As with `max_size`, replicas are ignored. To see the current shard size, use the `_cat shards` API. The `store` value shows the size of each shard, and `prirep` indicates whether a shard is a primary (`p`) or a replica (`r`). Optional.
+
+### `settings`
+
+The `settings` parameter specifies the index configuration options. See [Index settings](https://opensearch.org/docs/latest/install-and-configure/configuring-opensearch/index-settings/) for more information.
+
+## Example requests
+
+The following examples illustrate using the Rollover Index API. A rollover occurs when one or more of the specified conditions are met:
+
+- The index was created 5 or more days ago.
+- The index contains 500 or more documents.
+- The index's largest primary shard is 100 GB or larger.
+
+### Rolling over a data stream
+
+The following request rolls over the data stream if the current write index meets any of the specified conditions:
+
+```json
+POST my-data-stream/_rollover
+{
+  "conditions": {
+    "max_age": "5d",
+    "max_docs": 500,
+    "max_primary_shard_size": "100gb"
+  }
+}
+```
+{% include copy-curl.html %}
+
+### Rolling over an index alias with a write index
+
+The following request creates a date-time index and sets it as the write index for `my-alias`:
+
+```json
+PUT <my-index-{now/d}-000001>
+PUT %3Cmy-index-%7Bnow%2Fd%7D-000001%3E
+{
+  "aliases": {
+    "my-alias": {
+      "is_write_index": true
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+The next request performs a rollover using the alias:
+
+```json
+POST my-alias/_rollover
+{
+  "conditions": {
+    "max_age": "5d",
+    "max_docs": 500,
+    "max_primary_shard_size": "100gb"
+  }
+}
+```
+{% include copy-curl.html %}
+
+### Specifying settings during a rollover
+
+In most cases, you can use an index template to automatically configure the indexes created during a rollover operation. However, when rolling over an index alias, you can use the Rollover Index API to introduce additional index settings or override the settings defined in the template by sending the following request:
+
+```json
+POST my-alias/_rollover
+{
+  "settings": {
+    "index.number_of_shards": 4
+  }
+}
+```
+{% include copy-curl.html %}
+
+
+## Example response
+
+OpenSearch returns the following response confirming that all conditions except `max_primary_shard_size` were met:
+
+```json
+{
+  "acknowledged": true,
+  "shards_acknowledged": true,
+  "old_index": ".ds-my-data-stream-2029.06.11-000001",
+  "new_index": ".ds-my-data-stream-2029.06.12-000002",
+  "rolled_over": true,
+  "dry_run": false,
+  "conditions": {
+    "[max_age: 5d]": true,
+    "[max_docs: 500]": true,
+    "[max_primary_shard_size: 100gb]": false
+  }
+}
+```
+
+
+
+