[[settings]]
== Configuring Elasticsearch

Elasticsearch ships with good defaults and requires very little configuration.
Most settings can be changed on a running cluster using the
<<cluster-update-settings>> API.

The configuration files should contain settings which are node-specific (such
as `node.name` and paths), or settings which a node requires in order to be
able to join a cluster, such as `cluster.name` and `network.host`.

[[config-files-location]]
[discrete]
=== Config files location

Elasticsearch has three configuration files:

* `elasticsearch.yml` for configuring Elasticsearch
* `jvm.options` for configuring Elasticsearch JVM settings
* `log4j2.properties` for configuring Elasticsearch logging

These files are located in the config directory, whose default location depends
on whether or not the installation is from an archive distribution (`tar.gz` or
`zip`) or a package distribution (Debian or RPM packages).

For the archive distributions, the config directory location defaults to
`$ES_HOME/config`. The location of the config directory can be changed via the
`ES_PATH_CONF` environment variable as follows:

[source,sh]
-------------------------------
ES_PATH_CONF=/path/to/my/config ./bin/elasticsearch
-------------------------------

Alternatively, you can `export` the `ES_PATH_CONF` environment variable via the
command line or via your shell profile.

For the package distributions, the config directory location defaults to
`/etc/elasticsearch`. The location of the config directory can also be changed
via the `ES_PATH_CONF` environment variable, but note that setting this in your
shell is not sufficient. Instead, this variable is sourced from
`/etc/default/elasticsearch` (for the Debian package) and
`/etc/sysconfig/elasticsearch` (for the RPM package). You will need to edit the
`ES_PATH_CONF=/etc/elasticsearch` entry in one of these files accordingly to
change the config directory location.


[discrete]
=== Config file format

The configuration format is https://yaml.org/[YAML]. Here is an
example of changing the path of the data and logs directories:

[source,yaml]
--------------------------------------------------
path:
    data: /var/lib/elasticsearch
    logs: /var/log/elasticsearch
--------------------------------------------------

Settings can also be flattened as follows:

[source,yaml]
--------------------------------------------------
path.data: /var/lib/elasticsearch
path.logs: /var/log/elasticsearch
--------------------------------------------------

In YAML, you can format non-scalar values as sequences:

[source,yaml]
----
discovery.seed_hosts:
   - 192.168.1.10:9300
   - 192.168.1.11
   - seeds.mydomain.com
----

Though less common, you can also format non-scalar values as arrays:

[source,yaml]
----
discovery.seed_hosts: ["192.168.1.10:9300", "192.168.1.11", "seeds.mydomain.com"]
----

[discrete]
=== Environment variable substitution

Environment variables referenced with the `${...}` notation within the
configuration file will be replaced with the value of the environment
variable. For example:

[source,yaml]
--------------------------------------------------
node.name:    ${HOSTNAME}
network.host: ${ES_NETWORK_HOST}
--------------------------------------------------

Values for environment variables must be simple strings. Use a comma-separated string to provide values that Elasticsearch will parse as a list. For example, Elasticsearch will split the following string into a list of values for the `${HOSTNAME}` environment variable:

[source,yaml]
----
export HOSTNAME=“host1,host2"
----

[discrete]
[[cluster-setting-types]]
=== Cluster and node setting types

Cluster and node settings can be categorized based on how they are configured:

[[dynamic-cluster-setting]]
Dynamic::
+
--
You can configure and update dynamic settings on a running cluster using the
<<cluster-update-settings,cluster update settings API>>. You can also configure
dynamic settings locally on an unstarted or shut down node using
`elasticsearch.yml`.

Updates made using the cluster update settings API can be _persistent_, which
apply across cluster restarts, or _transient_, which reset after a cluster
restart. You can also reset transient or persistent settings by assigning them
a `null` value using the API.

If you configure the same setting using multiple methods, {es} applies the
settings in following order of precedence:

1. Transient setting
2. Persistent setting
3. `elasticsearch.yml` setting
4. Default setting value

For example, you can apply a transient setting to override a persistent setting
or `elasticsearch.yml` setting. However, a change to an `elasticsearch.yml`
setting will not override a defined transient or persistent setting.

TIP: It’s best to set dynamic, cluster-wide settings with the cluster update
settings API and use `elasticsearch.yml` only for local configurations. Using
the cluster update settings API ensures the setting is the same on all nodes. If
you accidentally configure different settings in `elasticsearch.yml` on
different nodes, it can be difficult to notice discrepancies.
--

[[static-cluster-setting]]
Static::
Static settings can only be configured on an unstarted or shut down node using
`elasticsearch.yml`.
+
Static settings must be set on every relevant node in the cluster.
