[[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.restclient]]
== Imperative Rest Client

To use the imperative (non-reactive) client, a configuration bean must be configured like this:

====
[source,java]
----
import org.springframework.data.elasticsearch.client.elc.ElasticsearchConfiguration;

@Configuration
public class MyClientConfig extends ElasticsearchConfiguration {

	@Override
	public ClientConfiguration clientConfiguration() {
		return ClientConfiguration.builder() //
			.connectedTo("localhost:9200") //
			.build();
	}
}

// ...

@Autowired
ElasticsearchOperations operations;      <.>

@Autowired 
ElasticsearchClient elasticsearchClient; <.>

@Autowired
RestClient restClient;                   <.>
----
the following can be injected:

<.> an implementation of `ElasticsearchOperations` 
<.> the `co.elastic.clients.elasticsearch.ElasticsearchClient` that is used. This is new Elasticsearch client 
implementation.
<.> the low level `RestClient` from the Elasticsearch libraries
====

Basically one should just use the `ElasticsearchOperations` to interact with the Elasticsearch cluster. When using 
repositories, this instance is used under the hood as well.

[[elasticsearch.clients.reactiverestclient]]
== Reactive Rest Client

When working with the reactive stack, the configuration must be derived from a different class:

====
[source,java]
----
import org.springframework.data.elasticsearch.client.elc.ReactiveElasticsearchConfiguration;

@Configuration
public class MyClientConfig extends ElasticsearchConfiguration {

	@Override
	public ClientConfiguration clientConfiguration() {
		return ClientConfiguration.builder() //
			.connectedTo("localhost:9200") //
			.build();
	}
}

// ...

@Autowired
ReactiveElasticsearchOperations operations;      <.>

@Autowired 
ReactiveElasticsearchClient elasticsearchClient; <.>

@Autowired
RestClient restClient;                           <.>
----
the following can be injected:

<.> an implementation of `ElasticsearchOperations`
<.> the `org.springframework.data.elasticsearch.client.elc.ReactiveElasticsearchClient` that is used. This is based 
on the new Elasticsearch client implementation.
<.> the low level `RestClient` from the Elasticsearch libraries
====

Basically one should just use the `ReactiveElasticsearchOperations` to interact with the Elasticsearch cluster. When 
using repositories, this instance is used under the hood as well.

[[elasticsearch.clients.resthighlevelclient]]
== High Level REST Client (deprecated)

The Java RestHighLevelClient is deprecated, but still can be configured like shown (read 
<<elasticsearch-migration-guide-4.4-5.0.old-client>> as well):

.RestHighLevelClient
====
[source,java]
----
import org.springframework.data.elasticsearch.client.erhlc.AbstractElasticsearchConfiguration;

@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")
  .id(randomID())
  .source(singletonMap("feature", "high-level-rest-client"))
  .setRefreshPolicy(IMMEDIATE);

IndexResponse response = highLevelClient.index(request,RequestOptions.DEFAULT);
----

<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 (deprecated)

The `org.springframework.data.elasticsearch.client.erhlc.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.

This was the first reactive implementation Spring Data Elasticsearch provided, but now is deprecated in favour of the `org.springframework.data.elasticsearch.client.elc.ReactiveElasticsearchClient`
which uses the functionality offered by the new Elasticsearch client libraries.

.Reactive REST Client (deprecated)
====
[source,java]
----
import org.springframework.data.elasticsearch.client.erhlc.AbstractReactiveElasticsearchConfiguration;

@Configuration
public class ReactiveRestClientConfig extends AbstractReactiveElasticsearchConfiguration {

    @Override
    @Bean
    public ReactiveElasticsearchClient reactiveElasticsearchClient() {
        final ClientConfiguration clientConfiguration = ClientConfiguration.builder() <.>
            .connectedTo("localhost:9200") //
            .build();
        return ReactiveRestClients.create(clientConfiguration);

    }
}
// ...

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

  request.index("spring-data")
    .id(randomID())
    .source(singletonMap("feature", "reactive-client"));
);
----

<.> Use the builder to provide cluster addresses, set default `HttpHeaders` or enable SSL.
====

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

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

.Client Configuration
====
[source,java]
----
HttpHeaders httpHeaders = new HttpHeaders();
httpHeaders.add("some-header", "on every request")                      <.>

ClientConfiguration clientConfiguration = ClientConfiguration.builder()
  .connectedTo("localhost:9200", "localhost:9291")                      <.>
  .usingSsl()                                                           <.>
  .withProxy("localhost:8888")                                          <.>
  .withPathPrefix("ela")                                                <.>
  .withConnectTimeout(Duration.ofSeconds(5))                            <.>
  .withSocketTimeout(Duration.ofSeconds(3))                             <.>
  .withDefaultHeaders(defaultHeaders)                                   <.>
  .withBasicAuth(username, password)                                    <.>
  .withHeaders(() -> {                                                  <.>
    HttpHeaders headers = new HttpHeaders();
    headers.add("currentTime", LocalDateTime.now().format(DateTimeFormatter.ISO_LOCAL_DATE_TIME));
    return headers;
  })
  .withClientConfigurer(                                                <.>
    ElasticsearchClients.ElasticsearchClientConfigurationCallback.from(clientBuilder -> {
  	  // ...
      return clientBuilder;
  	}))
  . // ... other options
  .build();

----

<.> Define default headers, if they need to be customized
<.> Use the builder to provide cluster addresses, set default `HttpHeaders` or enable SSL.
<.> Optionally enable SSL.
<.> Optionally set a proxy.
<.> Optionally set a path prefix, mostly used when different clusters a behind some reverse proxy.
<.> Set the connection timeout.
Default is 10 sec.
<.> Set the socket timeout.
Default is 5 sec.
<.> Optionally set headers.
<.> Add basic authentication.
<.> A `Supplier<Header>` function can be specified which is called every time before a request is sent to Elasticsearch - here, as an example, the current time is written in a header.
<.> a function configuring the low level REST client (the same for the imperative and reactive stack)
====

IMPORTANT: Adding a Header supplier as shown in above example allows to inject headers that may change over the time, like authentication JWT tokens.
If this is used in the reactive setup, the supplier function *must not* block!

=== Elasticsearch 7 compatibility headers

When using the deprecated `RestHighLevelClient` and accessing an Elasticsearch cluster that is running on version 8, it is necessary to set the compatibility headers
https://www.elastic.co/guide/en/elasticsearch/reference/8.0/rest-api-compatibility.html[see Elasticsearch 
documentation].

For the imperative client this must be done by setting the default headers, for the reactive code this must be done using a header supplier:

====
[source,java]
----

HttpHeaders compatibilityHeaders = new HttpHeaders();
compatibilityHeaders.add("Accept", "application/vnd.elasticsearch+json;compatible-with=7");
compatibilityHeaders.add("Content-Type", "application/vnd.elasticsearch+json;"
    + "compatible-with=7");

ClientConfiguration clientConfiguration = ClientConfiguration.builder()
    .connectedTo("localhost:9200")
    .withProxy("localhost:8080")
    .withBasicAuth("elastic","hcraescitsale")
    .withDefaultHeaders(compatibilityHeaders)    // this variant for imperative code
    .withHeaders(() -> compatibilityHeaders)     // this variant for reactive code
    .build();
		
----
====

[[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`.
