Add the documentation of create or update alias API

_api-reference/index-apis/update-alias.md

@@ -0,0 +1,83 @@
+---
+layout: default
+title: Create or update alias
+parent: Index APIs
+nav_order: 5
+---
+
+# Create or update alias
+**Introduced 1.0**
+{: .label .label-purple }
+
+You can use this API to add a data stream or index to an alias, or update the settings for an existing alias.
+
+
+## Example
+
+```json
+POST sample-index/_alias/sample-alias
+```
+
+```json
+POST sample-index/_alias/sample-alias
+{
+  "routing":"test"
+}
+```
+{% include copy-curl.html %}
+
+## Path and HTTP methods
+
+```
+POST /<target>/_alias/<alias-name>
+PUT /<target>/_alias/<alias-name>
+POST /_alias/<alias-name>
+PUT /_alias/<alias-name>
+POST /<target>/_aliases/<alias-name>
+PUT /<target>/_aliases/<alias-name>
+POST /_aliases/<alias-name>
+PUT /_aliases/<alias-name>
+POST /<target>/_aliases
+PUT /<target>/_aliases
+PUT /_alias
+```
+
+## Path parameters
+
+| Parameter | Data type | Description |
+:--- | :--- | :---
+| target | String | Comma-delimited list of data streams, indexes. Wildcard expressions (`*`) are supported. To target all data streams and indexes in a cluster, use `_all` or `*`. Optional. |
+| alias-name | String | The alias name to be created or updated. Optional. |
+
+## Query parameters
+
+All query parameters are optional.
+
+Parameter | Data Type | Description
+:--- | :--- | :---
+cluster_manager_timeout | Time | The amount of time to wait for a response from the cluster manager node. Default is `30s`.
+timeout | Time | The amount of time to wait for a response from the cluster. Default is `30s`.
+
+## Request body
+
+In the request body, you can specify the index name, the alias name, and the settings for the alias. All fields are optional.
+
+Field | Data Type | Description
+:--- | :--- | :--- | :---
+index | String | Comma-delimited list of data streams orindexes you want to associate with the alias. If this field is set, it will override the index name specified in the URL path.
+alias | String | The name of the alias. If this field is set, it will override the alias name specified in the URL path.
+is_write_index | Boolean | Specifies whether the index should be a write index. An alias can only have one write index at a time. If a write request is submitted to a alias that links to multiple indexes, OpenSearch executes the request only on the write index.
+routing | String | Used to assign a custom value to a shard for specific operations. 
+index_routing | String | Assigns a custom value to a shard only for index operations. 
+search_routing | String | Assigns a custom value to a shard only for search operations. 
+filter | Object | A filter to use with the alias, so the alias points to a filtered part of the index.
+
+## Response
+
+```json
+{
+    "acknowledged": true
+}
+```
+
+For more alias API operations, see [Index aliases]({{site.url}}{{site.baseurl}}/opensearch/index-alias/).