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 file locationedit

Elasticsearch has two configuration files:

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:

./bin/elasticsearch -Epath.conf=/path/to/my/config/

Config file formatedit

The configuration format is YAML. Here is an example of changing the path of the data and logs directories:

path:
    data: /var/lib/elasticsearch
    logs: /var/log/elasticsearch

Settings can also be flattened as follows:

path.data: /var/lib/elasticsearch
path.logs: /var/log/elasticsearch

Environment variable substitutionedit

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

node.name:    ${HOSTNAME}
network.host: ${ES_NETWORK_HOST}

Prompting for settingsedit

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:

node:
  name: ${prompt.text}

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

Enter value for [node.name]:

Setting default settingsedit

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:

./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.

Logging configurationedit

Elasticsearch uses 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.

appender.rolling.type = RollingFile 
appender.rolling.name = rolling
appender.rolling.fileName = ${sys:es.logs}.log 
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 
appender.rolling.policies.type = Policies
appender.rolling.policies.time.type = TimeBasedTriggeringPolicy 
appender.rolling.policies.time.interval = 1 
appender.rolling.policies.time.modulate = true 

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 Log4j documentation.

Deprecation loggingedit

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.

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 error.