[[sniffer]] == Sniffer Minimal library that allows to automatically discover nodes from a running Elasticsearch cluster and set them to an existing `RestClient` instance. It retrieves by default the nodes that belong to the cluster using the Nodes Info api and uses jackson to parse the obtained json response. Compatible with Elasticsearch 2.x and onwards. The low-level REST client is subject to the same release cycle as elasticsearch. Replace the version with the desired sniffer version, first released with `5.0.0-alpha4`. There is no relation between the sniffer version and the elasticsearch version that the client can communicate with. Sniffer supports fetching the nodes list from elasticsearch 2.x and onwards. === Maven coordinates Here is how you can configure the dependency using maven as a dependency manager. Add the following to your `pom.xml` file: ["source","xml",subs="attributes"] -------------------------------------------------- org.elasticsearch.client sniffer {version} -------------------------------------------------- === Gradle coordinates Here is how you can configure the dependency using gradle as a dependency manager. Add the following to your `build.gradle` file: ["source","groovy",subs="attributes"] -------------------------------------------------- dependencies { compile group: 'org.elasticsearch.client', name: 'sniffer', version: '{version}' } -------------------------------------------------- === Usage Once a `RestClient` instance has been created, a `Sniffer` can be associated to it. The `Sniffer` will make use of the provided `RestClient` to periodically (every 5 minutes by default) fetch the list of current nodes from the cluster and update them by calling `RestClient#setHosts`. [source,java] -------------------------------------------------- Sniffer sniffer = Sniffer.builder(restClient).build(); -------------------------------------------------- It is important to close the `Sniffer` so that its background thread gets properly shutdown and all of its resources are released. The `Sniffer` object should have the same lifecycle as the `RestClient` and get closed right before the client: [source,java] -------------------------------------------------- sniffer.close(); restClient.close(); -------------------------------------------------- The Elasticsearch Nodes Info api doesn't return the protocol to use when connecting to the nodes but only their `host:port` key-pair, hence `http` is used by default. In case `https` should be used instead, the `ElasticsearchHostsSniffer` object has to be manually created and provided as follows: [source,java] -------------------------------------------------- HostsSniffer hostsSniffer = new ElasticsearchHostsSniffer(restClient, ElasticsearchHostsSniffer.DEFAULT_SNIFF_REQUEST_TIMEOUT, ElasticsearchHostsSniffer.Scheme.HTTPS); Sniffer sniffer = Sniffer.builder(restClient) .setHostsSniffer(hostsSniffer).build(); -------------------------------------------------- In the same way it is also possible to customize the `sniffRequestTimeout`, which defaults to one second. That is the `timeout` parameter provided as a querystring parameter when calling the Nodes Info api, so that when the timeout expires on the server side, a valid response is still returned although it may contain only a subset of the nodes that are part of the cluster, the ones that have responsed until then. Also, a custom `HostsSniffer` implementation can be provided for advanced use-cases that may require fetching the hosts from external sources. The `Sniffer` updates the nodes by default every 5 minutes. This interval can be customized by providing it (in milliseconds) as follows: [source,java] -------------------------------------------------- Sniffer sniffer = Sniffer.builder(restClient) .setSniffIntervalMillis(60000).build(); -------------------------------------------------- It is also possible to enable sniffing on failure, meaning that after each failure the nodes list gets updated straightaway rather than at the following ordinary sniffing round. In this case a `SniffOnFailureListener` needs to be created at first and provided at `RestClient` creation. Also once the `Sniffer` is later created, it needs to be associated with that same `SniffOnFailureListener` instance, which will be notified at each failure and use the `Sniffer` to perform the additional sniffing round as described. [source,java] -------------------------------------------------- SniffOnFailureListener sniffOnFailureListener = new SniffOnFailureListener(); RestClient restClient = RestClient.builder(new HttpHost("localhost", 9200)) .setFailureListener(sniffOnFailureListener).build(); Sniffer sniffer = Sniffer.builder(restClient).build(); sniffOnFailureListener.setSniffer(sniffer); -------------------------------------------------- When using sniffing on failure, not only do the nodes get updated after each failure, but an additional sniffing round is also scheduled sooner than usual, by default one minute after the failure, assuming that things will go back to normal and we want to detect that as soon as possible. Said interval can be customized at `Sniffer` creation time as follows: [source,java] -------------------------------------------------- Sniffer sniffer = Sniffer.builder(restClient) .setSniffAfterFailureDelayMillis(30000).build(); -------------------------------------------------- Note that this last configuration parameter has no effect in case sniffing on failure is not enabled like explained above. === License Copyright 2013-2016 Elasticsearch Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.