[[elasticsearch.clients]]
= Elasticsearch Clients

This chapter illustrates configuration and usage of supported Elasticsearch client implementations.

Spring Data Elasticsearch operates upon an Elasticsearch client that is connected to a single Elasticsearch node or a cluster. Although the Elasticsearch Client can be used to work with the cluster, applications using Spring Data Elasticsearch normally use the higher level abstractions of <<elasticsearch.operations>> and <<elasticsearch.repositories>>.

[[elasticsearch.clients.transport]]
== Transport Client

WARNING: The well known `TransportClient` is deprecated as of Elasticsearch 7 and will be removed in Elasticsearch 8. (https://www.elastic.co/guide/en/elasticsearch/client/java-api/current/transport-client.html[see the Elasticsearch documentation]). Spring Data Elasticsearch will support the `TransportClient` as long as it is available in the used
Elasticsearch <<elasticsearch.versions,version>> but has deprecated the classes using it since version 4.0.

We strongly recommend to use the <<elasticsearch.clients.rest>> instead of the `TransportClient`.

.Transport Client
====
[source,java]
----
@Configuration
public class TransportClientConfig extends ElasticsearchConfigurationSupport {

    @Bean
    public Client elasticsearchClient() throws UnknownHostException {
        Settings settings = Settings.builder().put("cluster.name", "elasticsearch").build();        <1>
        TransportClient client = new PreBuiltTransportClient(settings);
        client.addTransportAddress(new TransportAddress(InetAddress.getByName("127.0.0.1"), 9300)); <2>
        return client;
    }

    @Bean(name = { "elasticsearchOperations", "elasticsearchTemplate" })
    public ElasticsearchTemplate elasticsearchTemplate() throws UnknownHostException {
        return new ElasticsearchTemplate(elasticsearchClient());
    }
}

// ...

IndexRequest request = new IndexRequest("spring-data", "elasticsearch", randomID())
 .source(someObject)
 .setRefreshPolicy(IMMEDIATE);

IndexResponse response = client.index(request);
----
<1> The `TransportClient` must be configured with the cluster name.
<2> The host and port to connect the client to.
====

[[elasticsearch.clients.rest]]
== High Level REST Client

The Java High Level REST Client is the default client of Elasticsearch, it provides a straight forward replacement for the `TransportClient` as it accepts and returns
the very same request/response objects and therefore depends on the Elasticsearch core project.
Asynchronous calls are operated upon a client managed thread pool and require a callback to be notified when the request is done.

.High Level REST Client
====
[source,java]
----
@Configuration
public class RestClientConfig extends AbstractElasticsearchConfiguration {

    @Override
    @Bean
    public RestHighLevelClient elasticsearchClient() {

        final ClientConfiguration clientConfiguration = ClientConfiguration.builder()  <1>
            .connectedTo("localhost:9200")
            .build();

        return RestClients.create(clientConfiguration).rest();                         <2>
    }
}

// ...

  @Autowired
  RestHighLevelClient highLevelClient;

  RestClient lowLevelClient = highLevelClient.lowLevelClient();                        <3>

// ...

IndexRequest request = new IndexRequest("spring-data", "elasticsearch", randomID())
  .source(singletonMap("feature", "high-level-rest-client"))
  .setRefreshPolicy(IMMEDIATE);

IndexResponse response = highLevelClient.index(request);
----
<1> Use the builder to provide cluster addresses, set default `HttpHeaders` or enable SSL.
<2> Create the RestHighLevelClient.
<3> It is also possible to obtain the `lowLevelRest()` client.
====

[[elasticsearch.clients.reactive]]
== Reactive Client

The `ReactiveElasticsearchClient` is a non official driver based on `WebClient`.
It uses the request/response objects provided by the Elasticsearch core project.
Calls are directly operated on the reactive stack, **not** wrapping async (thread pool bound) responses into reactive types.

.Reactive REST Client
====
[source,java]
----
static class Config {

  @Bean
  ReactiveElasticsearchClient client() {

    ClientConfiguration clientConfiguration = ClientConfiguration.builder() <1>
      .connectedTo("localhost:9200", "localhost:9291")
      .build();

    return ReactiveRestClients.create(clientConfiguration);
  }
}

// ...

Mono<IndexResponse> response = client.index(request ->

  request.index("spring-data")
    .type("elasticsearch")
    .id(randomID())
    .source(singletonMap("feature", "reactive-client"))
    .setRefreshPolicy(IMMEDIATE);
);
----
<1> Use the builder to provide cluster addresses, set default `HttpHeaders` or enable SSL.
====

NOTE: The ReactiveClient response, especially for search operations, is bound to the `from` (offset) & `size` (limit) options of the request.

[[elasticsearch.clients.configuration]]
== Client Configuration

Client behaviour can be changed via the `ClientConfiguration` that allows to set options for SSL, connect and socket timeouts.

.Client Configuration
====
[source,java]
----
// optional if Basic Auhtentication is needed
HttpHeaders httpHeaders = new HttpHeaders();
httpHeaders.add("es-security-runas-user", "some-user")                  <1>

ClientConfiguration clientConfiguration = ClientConfiguration.builder()
  .connectedTo("localhost:9200", "localhost:9291")                      <2>
  .withProxy("localhost:8888")                                          <3>
  .withPathPrefix("ela")                                                <4>
  .withConnectTimeout(Duration.ofSeconds(5))                            <5>
  .withSocketTimeout(Duration.ofSeconds(3))                             <6>
  .useSsl()                                                             <7>
  .withDefaultHeaders(defaultHeaders)                                   <8>
  .withBasicAuth(username, password)                                    <9>
  . // ... other options
  .build();

----
<1> Define default headers, if they need to be customized
<2> Use the builder to provide cluster addresses, set default `HttpHeaders` or enable SSL.
<3> Optionally set a proxy footnote:notreactive[not yet implemented for the reactive client].
<4> Optionally set a path prefix, mostly used when different clusters a behind some reverse proxy.
<5> Set the connection timeout. Default is 10 sec.
<6> Set the socket timeout. Default is 5 sec.
<7> Optionally enable SSL.
<8> Optionally set headers.
<9> Add basic authentication.
====

[[elasticsearch.clients.logging]]
== Client Logging

To see what is actually sent to and received from the server `Request` / `Response` logging on the transport level needs
to be turned on as outlined in the snippet below.

.Enable transport layer logging
[source,xml]
----
<logger name="org.springframework.data.elasticsearch.client.WIRE" level="trace"/>
----

NOTE: The above applies to both the `RestHighLevelClient` and `ReactiveElasticsearchClient` when obtained via `RestClients` respectively `ReactiveRestClients`, is not available for the `TransportClient`.