[[logging]]
=== Logging

include::{es-repo-dir}/tab-widgets/code.asciidoc[]

You can use {es}'s application logs to monitor your cluster and diagnose issues.
If you run {es} as a service, the default location of the logs varies based on
your platform and installation method:

include::{es-repo-dir}/tab-widgets/logging-widget.asciidoc[]

If you run {es} from the command line, {es} prints logs to the standard output
(`stdout`).

[discrete]
[[loggin-configuration]]
=== Logging configuration

Elasticsearch uses https://logging.apache.org/log4j/2.x/[Log4j 2] for
logging. Log4j 2 can be configured using the log4j2.properties
file. Elasticsearch exposes three properties, `${sys:es.logs.base_path}`,
`${sys:es.logs.cluster_name}`, and `${sys:es.logs.node_name}` that can be
referenced in the configuration file to determine the location of the log
files. The property `${sys:es.logs.base_path}` will resolve to the log directory,
`${sys:es.logs.cluster_name}` will resolve to the cluster name (used as the
prefix of log filenames in the default configuration), and
`${sys:es.logs.node_name}` will resolve to the node name (if the node name is
explicitly set).

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

[source,properties]
--------------------------------------------------
######## Server JSON ############################
appender.rolling.type = RollingFile <1>
appender.rolling.name = rolling
appender.rolling.fileName = ${sys:es.logs.base_path}${sys:file.separator}${sys:es.logs.cluster_name}_server.json <2>
appender.rolling.layout.type = ECSJsonLayout <3>
appender.rolling.layout.dataset = elasticsearch.server <4>
appender.rolling.filePattern = ${sys:es.logs.base_path}${sys:file.separator}${sys:es.logs.cluster_name}-%d{yyyy-MM-dd}-%i.json.gz <5>
appender.rolling.policies.type = Policies
appender.rolling.policies.time.type = TimeBasedTriggeringPolicy <6>
appender.rolling.policies.time.interval = 1 <7>
appender.rolling.policies.time.modulate = true <8>
appender.rolling.policies.size.type = SizeBasedTriggeringPolicy <9>
appender.rolling.policies.size.size = 256MB <10>
appender.rolling.strategy.type = DefaultRolloverStrategy
appender.rolling.strategy.fileIndex = nomax
appender.rolling.strategy.action.type = Delete <11>
appender.rolling.strategy.action.basepath = ${sys:es.logs.base_path}
appender.rolling.strategy.action.condition.type = IfFileName <12>
appender.rolling.strategy.action.condition.glob = ${sys:es.logs.cluster_name}-* <13>
appender.rolling.strategy.action.condition.nested_condition.type = IfAccumulatedFileSize <14>
appender.rolling.strategy.action.condition.nested_condition.exceeds = 2GB <15>
################################################
--------------------------------------------------

<1> Configure the `RollingFile` appender
<2> Log to `/var/log/elasticsearch/production_server.json`
<3> Use JSON layout.
<4> `dataset` is a flag populating the `event.dataset` field in a `ECSJsonLayout`.
 It can be used to distinguish different types of logs more easily when parsing them.
<5> Roll logs to `/var/log/elasticsearch/production-yyyy-MM-dd-i.json`; logs
    will be compressed on each roll and `i` will be incremented
<6> Use a time-based roll policy
<7> Roll logs on a daily basis
<8> Align rolls on the day boundary (as opposed to rolling every twenty-four
    hours)
<9> Using a size-based roll policy
<10> Roll logs after 256 MB
<11> Use a delete action when rolling logs
<12> Only delete logs matching a file pattern
<13> The pattern is to only delete the main logs
<14> Only delete if we have accumulated too many compressed logs
<15> The size condition on the compressed logs is 2 GB

[source,properties]
--------------------------------------------------
######## Server -  old style pattern ###########
appender.rolling_old.type = RollingFile
appender.rolling_old.name = rolling_old
appender.rolling_old.fileName = ${sys:es.logs.base_path}${sys:file.separator}${sys:es.logs.cluster_name}_server.log <1>
appender.rolling_old.layout.type = PatternLayout
appender.rolling_old.layout.pattern = [%d{ISO8601}][%-5p][%-25c{1.}] [%node_name]%marker %m%n
appender.rolling_old.filePattern = ${sys:es.logs.base_path}${sys:file.separator}${sys:es.logs.cluster_name}-%d{yyyy-MM-dd}-%i.old_log.gz

--------------------------------------------------
<1> The configuration for `old style` pattern appenders. These logs will be saved in `*.log` files and if archived will be in `*
.log.gz` files. Note that these should be considered deprecated and will be removed in the future.

NOTE: Log4j's configuration parsing gets confused by any extraneous whitespace;
if you copy and paste any Log4j settings on this page, or enter any Log4j
configuration in general, be sure to trim any leading and trailing whitespace.

Note than you can replace `.gz` by `.zip` in `appender.rolling.filePattern` to
compress the rolled logs using the zip format. If you remove the `.gz`
extension then logs will not be compressed as they are rolled.

If you want to retain log files for a specified period of time, you can use a
rollover strategy with a delete action.

[source,properties]
--------------------------------------------------
appender.rolling.strategy.type = DefaultRolloverStrategy <1>
appender.rolling.strategy.action.type = Delete <2>
appender.rolling.strategy.action.basepath = ${sys:es.logs.base_path} <3>
appender.rolling.strategy.action.condition.type = IfFileName <4>
appender.rolling.strategy.action.condition.glob = ${sys:es.logs.cluster_name}-* <5>
appender.rolling.strategy.action.condition.nested_condition.type = IfLastModified <6>
appender.rolling.strategy.action.condition.nested_condition.age = 7D <7>
--------------------------------------------------

<1> Configure the `DefaultRolloverStrategy`
<2> Configure the `Delete` action for handling rollovers
<3> The base path to the Elasticsearch logs
<4> The condition to apply when handling rollovers
<5> Delete files from the base path matching the glob
    `${sys:es.logs.cluster_name}-*`; this is the glob that log files are rolled
    to; this is needed to only delete the rolled Elasticsearch logs but not also
    delete the deprecation and slow logs
<6> A nested condition to apply to files matching the glob
<7> Retain logs for seven days

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
https://logging.apache.org/log4j/2.x/manual/configuration.html[Log4j
documentation].

[discrete]
[[configuring-logging-levels]]
=== Configuring logging levels

Each Java package in the {es-repo}[{es} source code] has a related logger. For
example, the `org.elasticsearch.discovery` package has
`logger.org.elasticsearch.discovery` for logs related to the
<<modules-discovery-hosts-providers,discovery>> process.

To get more or less verbose logs, use the <<cluster-update-settings,cluster
update settings API>> to change the related logger's log level. Each logger
accepts Log4j 2's built-in log levels, from least to most verbose: `OFF`,
`FATAL`, `ERROR`, `WARN`, `INFO`, `DEBUG`, and `TRACE`. The default log level is
`INFO`. Messages logged at higher verbosity levels (`DEBUG` and `TRACE`) are
only intended for expert use.

[source,console]
----
PUT /_cluster/settings
{
  "transient": {
    "logger.org.elasticsearch.discovery": "DEBUG"
  }
}
----

Other ways to change log levels include:

1. `elasticsearch.yml`:
+
--
[source,yaml]
----
logger.org.elasticsearch.discovery: DEBUG
----

This is most appropriate when debugging a problem on a single node.
--

2. `log4j2.properties`:
+
--
[source,properties]
----
logger.discovery.name = org.elasticsearch.discovery
logger.discovery.level = debug
----

This is most appropriate when you already need to change your Log4j 2
configuration for other reasons. For example, you may want to send logs for a
particular logger to another file. However, these use cases are rare.
--

[discrete]
[[deprecation-logging]]
=== Deprecation logging

{es} also writes deprecation logs to the log directory. These logs record a
message when you use deprecated {es} functionality. You can use the deprecation
logs to update your application before upgrading {es} to a new major version.

By default, {es} rolls and compresses deprecation logs at 1GB. The default
configuration preserves a maximum of five log files: four rolled logs and an
active log.

{es} emits deprecation log messages at the `CRITICAL` level. Those messages
are indicating that a used deprecation feature will be removed in a next major
version. Deprecation log messages at the `WARN` level indicates that a less
critical feature was used, it won't be removed in next major version, but might
be removed in the future.

To stop writing deprecation log messages, set `logger.deprecation.level`
to `OFF`:

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

You can identify what is triggering deprecated functionality if `X-Opaque-Id` was used as an HTTP header.
The user ID is included in the `X-Opaque-ID` field in deprecation JSON logs.

[source,js]
---------------------------
{
  "type": "deprecation",
  "timestamp": "2019-08-30T12:07:07,126+02:00",
  "level": "WARN",
  "component": "o.e.d.r.a.a.i.RestCreateIndexAction",
  "cluster.name": "distribution_run",
  "node.name": "node-0",
  "message": "[types removal] Using include_type_name in create index requests is deprecated. The parameter will be removed in the next major version.",
  "x-opaque-id": "MY_USER_ID",
  "cluster.uuid": "Aq-c-PAeQiK3tfBYtig9Bw",
  "node.id": "D7fUYfnfTLa2D7y-xw6tZg"
}
---------------------------
// NOTCONSOLE

Deprecation logs can be indexed into `.logs-deprecation.elasticsearch-default` data stream
`cluster.deprecation_indexing.enabled` setting is set to true.

==== Deprecation logs throttling
Deprecation logs are deduplicated based on a deprecated feature key
and x-opaque-id so that if a feature is repeatedly used, it will not overload the deprecation logs.
This applies to both indexed deprecation logs and logs emitted to log files.
You can disable the use of `x-opaque-id` in throttling by changing
`cluster.deprecation_indexing.x_opaque_id_used.enabled` to false
See link:./server/src/main/java/org/elasticsearch/common/logging/RateLimitingFilter.java[RateLimitingFilter]

[discrete]
[[json-logging]]
=== JSON log format

To make parsing Elasticsearch logs easier, logs are now printed in a JSON format.
This is configured by a Log4J layout property `appender.rolling.layout.type = ECSJsonLayout`.
This layout requires a `dataset` attribute to be set which is used to distinguish
logs streams when parsing.
[source,properties]
--------------------------------------------------
appender.rolling.layout.type = ECSJsonLayout
appender.rolling.layout.dataset = elasticsearch.server
--------------------------------------------------
:es-json-layout-java-doc: {elasticsearch-javadoc}/org/elasticsearch/common/logging/ESJsonLayout.html

Each line contains a single JSON document with the properties configured in `ECSJsonLayout`.
See this class {es-json-layout-java-doc}[javadoc] for more details.
However if a JSON document contains an exception, it will be printed over multiple lines.
The first line will contain regular properties and subsequent lines will contain the
stacktrace formatted as a JSON array.


NOTE: You can still use your own custom layout. To do that replace the line
`appender.rolling.layout.type` with a different layout. See sample below:
[source,properties]
--------------------------------------------------
appender.rolling.type = RollingFile
appender.rolling.name = rolling
appender.rolling.fileName = ${sys:es.logs.base_path}${sys:file.separator}${sys:es.logs.cluster_name}_server.log
appender.rolling.layout.type = PatternLayout
appender.rolling.layout.pattern = [%d{ISO8601}][%-5p][%-25c{1.}] [%node_name]%marker %.-10000m%n
appender.rolling.filePattern = ${sys:es.logs.base_path}${sys:file.separator}${sys:es.logs.cluster_name}-%d{yyyy-MM-dd}-%i.log.gz
--------------------------------------------------
