chore(elasticsearch sink): Add documentation and tests about OpenSearch (#23603)

* Mention OpenSearch compatibility in the doc

* Add OpenSearch config unit tests

* cargo vdev fmt
* Remove trailing spaces

---------

Co-authored-by: Pavlos Rontidis <[email protected]>

Author: taisho6339

src/sinks/elasticsearch/config.rs

@@ -690,4 +690,70 @@ mod tests {
         assert_eq!(config.mode, ElasticsearchMode::Bulk);
         assert_eq!(config.bulk, BulkConfig::default());
     }
+
+    #[test]
+    fn parse_opensearch_service_type_managed() {
+        let config = toml::from_str::<ElasticsearchConfig>(
+            r#"
+            endpoints = [""]
+            opensearch_service_type = "managed"
+        "#,
+        )
+        .unwrap();
+        assert_eq!(
+            config.opensearch_service_type,
+            OpenSearchServiceType::Managed
+        );
+    }
+
+    #[test]
+    fn parse_opensearch_service_type_serverless() {
+        let config = toml::from_str::<ElasticsearchConfig>(
+            r#"
+            endpoints = [""]
+            opensearch_service_type = "serverless"
+            auth.strategy = "aws"
+            api_version = "auto"
+        "#,
+        )
+        .unwrap();
+        assert_eq!(
+            config.opensearch_service_type,
+            OpenSearchServiceType::Serverless
+        );
+    }
+
+    #[test]
+    fn parse_opensearch_service_type_default() {
+        let config = toml::from_str::<ElasticsearchConfig>(
+            r#"
+            endpoints = [""]
+        "#,
+        )
+        .unwrap();
+        assert_eq!(
+            config.opensearch_service_type,
+            OpenSearchServiceType::Managed
+        );
+    }
+
+    #[cfg(feature = "aws-core")]
+    #[test]
+    fn parse_opensearch_serverless_with_aws_auth() {
+        let config = toml::from_str::<ElasticsearchConfig>(
+            r#"
+            endpoints = [""]
+            opensearch_service_type = "serverless"
+            auth.strategy = "aws"
+            api_version = "auto"
+        "#,
+        )
+        .unwrap();
+        assert_eq!(
+            config.opensearch_service_type,
+            OpenSearchServiceType::Serverless
+        );
+        assert!(matches!(config.auth, Some(ElasticsearchAuthConfig::Aws(_))));
+        assert_eq!(config.api_version, ElasticsearchApiVersion::Auto);
+    }
 }

website/cue/reference/components/sinks/elasticsearch.cue

@@ -71,7 +71,13 @@ components: sinks: elasticsearch: {
 				"""#,
 		]
 		warnings: []
-		notices: []
+		notices: [
+			#"""
+				This sink is compatible with OpenSearch, including both self-managed OpenSearch instances
+				and Amazon OpenSearch Service. For OpenSearch Serverless, set `opensearch_service_type = "serverless"`
+				and use AWS authentication.
+				"""#,
+		]
 	}
 
 	configuration: generated.components.sinks.elasticsearch.configuration
@@ -160,6 +166,34 @@ components: sinks: elasticsearch: {
 				"""
 		}
 
+		opensearch_compatibility: {
+			title: "OpenSearch Compatibility"
+			body: """
+				This sink is fully compatible with OpenSearch, which is an open-source fork of Elasticsearch.
+				Vector can connect to:
+
+				- **Self-managed OpenSearch**: Use the same configuration as Elasticsearch with `opensearch_service_type = "managed"` (default)
+				- **Amazon OpenSearch Service**: Configure AWS authentication and set `opensearch_service_type = "managed"`
+				- **Amazon OpenSearch Serverless**: Set `opensearch_service_type = "serverless"` and use AWS authentication
+
+				All Elasticsearch sink features are supported with OpenSearch, including:
+				- Bulk indexing and data streams
+				- Authentication (Basic, AWS)
+				- TLS/SSL encryption
+				- Automatic API version detection
+				- Compression and custom headers
+
+				Example configuration for OpenSearch:
+				```toml
+				[sinks.opensearch]
+				type = "elasticsearch"
+				endpoints = ["https://opensearch.example.com:9200"]
+				opensearch_service_type = "managed"
+				# ... other configuration options
+				```
+				"""
+		}
+
 		aws_authentication: components._aws.how_it_works.aws_authentication
 	}
 }