[[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.

WARNING: The well known `TransportClient` is deprecated as of Elasticsearch 7.0.0 and is expected to be removed in Elasticsearch 8.0.

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

The Java High Level REST Client 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]
----
static class Config {

  @Bean
  RestHighLevelClient client() {

    ClientConfiguration clientConfiguration = ClientConfiguration.builder() <1>
      .connectedTo("localhost:9200", "localhost:9201")
      .build();

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

// ...

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

IndexResponse response = client.index(request);
----
<1> Use the builder to provide cluster addresses, set default `HttpHeaders` or enbale SSL.
<2> Next to the `rest()` client 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 enbale 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]
----

ClientConfiguration clientConfiguration = ClientConfiguration.builder()
  .connectedTo("localhost:9200", "localhost:9291") <1>
  .withConnectTimeout(Duration.ofSeconds(5)) <2>
  .withSocketTimeout(Duration.ofSeconds(3)) <3>
  .useSsl()
  . // ... other options
  .build();

----
<1> Use the builder to provide cluster addresses, set default `HttpHeaders` or enbale SSL.
<2> Set the connection timeout. Default is 10 sec.
<3> Set the socket timeout. Default is 5 sec.
====

[[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`.