nextcloud-docs/elasticsearch/content.md

What is Elasticsearch?

Elasticsearch is a search server based on Lucene. It provides a distributed, multitenant-capable full-text search engine with a RESTful web interface and schema-free JSON documents.

Elasticsearch is a registered trademark of Elasticsearch BV.

wikipedia.org/wiki/Elasticsearch

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How to use this image

Cluster

Note: since 5.0, Elasticsearch only listens on localhost by default on both http and transport, so this image sets http.host to 0.0.0.0 (given that localhost is not terribly useful in the Docker context).

As a result, this image does not support clustering out of the box and extra configuration must be set in order to support it.

Supporting clustering imply having Elasticsearch in a production mode which is more strict about the bootstrap checks that it performs, especially when checking the value of vm.max_map_count which is not namespaced and thus must be set to an acceptable value on the host (as opposed to simply using --sysctl on docker run).

See the following sections of the upstream documentation for more information:

• Setup Elasticsearch » Important System Configuration » Virtual memory
• Setup Elasticsearch » Bootstrap Checks » Maximum map count check

This comment in elastic/elasticsearch#4978 shows why this change was added in upstream.

Elasticsearch will not start in production mode if vm.max_map_count is not high enough. [...] If the value on your system is NOT high enough, then your cluster is going to crash and burn at some stage and you will lose data.

Running Containers

You can run the default elasticsearch command simply:

$ docker run -d elasticsearch

You can also pass in additional flags to elasticsearch:

$ docker run -d elasticsearch -Des.node.name="TestNode"

This image comes with a default set of configuration files for elasticsearch, but if you want to provide your own set of configuration files, you can do so via a volume mounted at /usr/share/elasticsearch/config:

$ docker run -d -v "$PWD/config":/usr/share/elasticsearch/config elasticsearch

This image is configured with a volume at /usr/share/elasticsearch/data to hold the persisted index data. Use that path if you would like to keep the data in a mounted volume:

$ docker run -d -v "$PWD/esdata":/usr/share/elasticsearch/data elasticsearch

This image includes EXPOSE 9200 9300 (default http.port), so standard container linking will make it automatically available to the linked containers.