OpenSearch/docs/reference/setup/configuration.asciidoc

[[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`.

[float]
=== Config file location

Elasticsearch has two configuration files:

* `elasticsearch.yml` for configuring Elasticsearch, and
* `log4j2.properties` for configuring Elasticsearch logging.

These files are located in the config directory, whose location defaults to
`$ES_HOME/config/`.  The Debian and RPM packages set the config directory
location to `/etc/elasticsearch/`.

The location of the config directory can be changed with the `path.conf`
setting, as follows:

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

[float]
=== Config file format

The configuration format is http://www.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
--------------------------------------------------

[float]
=== Environment variable subsitution

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

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

[float]
=== Prompting for settings

For settings that you do not wish to store in the configuration file, you can
use the value `${prompt.text}` or `${prompt.secret}` and start Elasticsearch
in the foreground. `${prompt.secret}` has echoing disabled so that the value
entered will not be shown in your terminal; `${prompt.text}` will allow you to
see the value as you type it in. For example:

[source,yaml]
--------------------------------------------------
node:
  name: ${prompt.text}
--------------------------------------------------

When starting Elasticsearch, you will be prompted to enter the actual value
like so:

[source,sh]
--------------------------------------------------
Enter value for [node.name]:
--------------------------------------------------

NOTE: Elasticsearch will not start if `${prompt.text}` or `${prompt.secret}`
is used in the settings and the process is run as a service or in the background.

[float]
=== Setting default settings

New default settings may be specified on the command line using the
`default.` prefix.  This will specify a value that will be used by
default unless another value is specified in the config file.

For instance, if Elasticsearch is started as follows:

[source,sh]
---------------------------
./bin/elasticsearch -Edefault.node.name=My_Node
---------------------------

the value for `node.name` will be `My_Node`, unless it is overwritten on the
command line with `es.node.name` or in the config file with `node.name`.

[float]
[[logging]]
== Logging configuration

Elasticsearch uses http://logging.apache.org/log4j/2.x/[Log4j 2] for
logging. Log4j 2 can be configured using the log4j2.properties
file. Elasticsearch exposes a single property `${sys:es.logs}` that can be
referenced in the configuration file to determine the location of the log files;
this will resolve to a prefix for the Elasticsearch log file at runtime.

For example, if your log directory (`path.logs`) is `/var/log/elasticsearch` and
your cluster is named `production` then `${sys:es.logs}` will resolve to
`/var/log/elasticsearch/production`.

[source,properties]
--------------------------------------------------
appender.rolling.type = RollingFile <1>
appender.rolling.name = rolling
appender.rolling.fileName = ${sys:es.logs}.log <2>
appender.rolling.layout.type = PatternLayout
appender.rolling.layout.pattern = [%d{ISO8601}][%-5p][%-25c] %.10000m%n
appender.rolling.filePattern = ${sys:es.logs}-%d{yyyy-MM-dd}.log <3>
appender.rolling.policies.type = Policies
appender.rolling.policies.time.type = TimeBasedTriggeringPolicy <4>
appender.rolling.policies.time.interval = 1 <5>
appender.rolling.policies.time.modulate = true <6>
--------------------------------------------------

<1> Configure the `RollingFile` appender
<2> Log to `/var/log/elasticsearch/production.log`
<3> Roll logs to `/var/log/elasticsearch/production-yyyy-MM-dd.log`
<4> Using a time-based roll policy
<5> Roll logs on a daily basis
<6> Align rolls on the day boundary (as opposed to rolling every twenty-four
    hours)

If you append `.gz` or `.zip` to `appender.rolling.filePattern`, then the logs
will be compressed as they are rolled.

Multiple configuration files can be loaded (in which case they will get merged)
as long as they are named `log4j2.properties` and have the Elasticsearch config
directory as an ancestor; this is useful for plugins that expose additional
loggers. The logger section contains the java packages and their corresponding
log level. The appender section contains the destinations for the logs.
Extensive information on how to customize logging and all the supported
appenders can be found on the
http://logging.apache.org/log4j/2.x/manual/configuration.html[Log4j
documentation].

[float]
[[deprecation-logging]]
=== Deprecation logging

In addition to regular logging, Elasticsearch allows you to enable logging
of deprecated actions. For example this allows you to determine early, if
you need to migrate certain functionality in the future. By default,
deprecation logging is enabled at the WARN level, the level at which all
deprecation log messages will be emitted.

[source,properties]
--------------------------------------------------
logger.deprecation.level = warn
--------------------------------------------------

This will create a daily rolling deprecation log file in your log directory.
Check this file regularly, especially when you intend to upgrade to a new
major version.

The default logging configuration has set the roll policy for the deprecation
logs to roll and compress after 1 GB, and to preserve a maximum of five log
files (four rolled logs, and the active log).

You can disable it in the `config/log4j2.properties` file by setting the deprecation
log level to `info`.