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