Create java RestHighLevelClient in elastic cluster mode - elasticsearch

Question

If elasticsearch runs on single mode, I can easily establish the RestHighLevel connection with this line of code:
RestHighLevelClient client = new RestHighLevelClient(
RestClient.builder(
new HttpHost("localhost", 9200, "http"),
new HttpHost("localhost", 9201, "http")));
But if my elastic cluster has 3 machines, e.g., "host1", "host2", "host3", how to create the rest high level client in cluster mode ?
Thanks

Answer 1

RestHighLevelClient client = new RestHighLevelClient(
RestClient.builder(
new HttpHost("host1", 9200, "http"),
new HttpHost("host2", 9200, "http"),
new HttpHost("host2", 9200, "http")
)
);
As the doc it looks like you were referencing states, RestClient.builder accepts an array of HttpHosts to connect to. The client (which under the hood is the ES low-level REST client) will round-robin requests to these hosts. See also the Javadoc.

Answer 2

As per the Elasticsearch docs you can pass multiple Elasticsearch hosts in RestClient.builder().
The better solution is to load the Elasticsearch hosts from configuration(application.conf in case of Scala-based application) instead of hardcoding it in the codebase.
Here is the Scala-based solution using Java Varargs(:_*).
application.conf
es_hosts = ["x.x.x.x","x.x.x.x","x.x.x.x"] // You can even use service-name/service-discovery
es_port = 9200
es_scheme = "http"
Code snippet
import collection.JavaConverters._
import com.typesafe.config.ConfigFactory
import org.apache.http.HttpHost
import org.elasticsearch.client.{RestClient, RestHighLevelClient}
val config = ConfigFactory.load()
val port = config.getInt(ES_PORT)
val scheme = config.getString(ES_SCHEME)
val es_hosts = config.getStringList(ES_HOSTS).asScala
val httpHosts = es_hosts.map(host => new HttpHost(host, port, scheme))
val low_level_client = RestClient.builder(httpHosts:_*)
val high_level_client: RestHighLevelClient = new RestHighLevelClient(low_level_client)

Answer 3

To create High level REST client using multiple hosts, you can do something like following:
String[] esHosts = new String[]{"node1-example.com:9200", "node2-example.com:9200",
"node3-example.com:9200"};
final ClientConfiguration clientConfiguration = ClientConfiguration.builder()
.connectedTo(esHosts)
.build();
RestHighLevelClient restClient = RestClients.create(clientConfiguration).rest();
// Hostnames used for building client can be verified as following
List<Node> nodes = restClient.getLowLevelClient().getNodes();
nodes.forEach(node -> System.out.println(node.toString()));
References:
Docs for High Level REST Client
Source code for ClientConfigurationBuilder

Answer 4

I am creating my elastic REST client with below steps:
RestHighLevelClient client=null;
List<HttpHost> hostList = new ArrayList<>();
for (String host : hosts) {
String[] hostDetails = host.split("\\:");hostList.add(new
HttpHost(hostDetails[0],Integer.parseInt(hostDetails[1]),https));
}
try(RestHighLevelClient client1 = new RestHighLevelClient(
RestClient.builder(hostList.toArray(new
HttpHost[hostList.size()]))
.setHttpClientConfigCallback(
httpClientBuilder ->
// to do this only if auth is enabled
httpClientBuilder.setDefaultCredentialsProvider(credentialsProvider))))
{
client = client1;
}
} catch (IOException e) {
log.error("exception occurred while setting elastic client");
}