Mastodon supports full-text search when ElasticSearch is available. Mastodon’s full-text search allows logged in users to find results from their own statuses, their mentions, their favourites, and their bookmarks. It deliberately does not allow searching for arbitrary strings in the entire database.
**Security warning:** By default, ElasticSearch is supposed to bind to localhost only, i.e. be inaccessible from the outside network. You can check which address ElasticSearch binds to by looking at `network.host` within `/etc/elasticsearch/elasticsearch.yml`. Consider that anyone who can access ElasticSearch can access and modify any data within it, as there is no authentication layer. So it’s really important that the access is secured. Having a firewall that only exposes the 22, 80 and 443 ports is advisable, as outlined in the [main installation instructions](../../prerequisites/#install-a-firewall-and-only-whitelist-ssh-http-and-https-ports). If you have a multi-host setup, you must know how to secure internal traffic.
**Security warning:** ElasticSearch versions between `2.0` and `2.14.1` are affected by an [exploit](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-44228) in the `log4j` library. If affected, please refer to the [temporary mitigation](https://github.com/elastic/elasticsearch/issues/81618#issuecomment-991000240) from the ElasticSearch issue tracker.
If you have multiple Mastodon servers on the same machine, and you are planning to use the same ElasticSearch installation for all of them, make sure that all of them have unique `REDIS_NAMESPACE` in their configurations, to differentiate the indices. If you need to override the prefix of the ElasticSearch indices, you can set `ES_PREFIX` directly.
The default analyzer of the ElasticSearch is the standard analyzer, which may not be the best especially for Chinese. To improve search experience, you can install a language specific analyzer. Before creating the indices in ElasticSearch, install the following ElasticSearch extensions: