Logging
editLogging
editLogstash emits internal logs during its operation, which are placed in LS_HOME/logs (or /var/log/logstash for
DEB/RPM). The default logging level is INFO. Logstash’s logging framework is based on
Log4j 2 framework, and much of its functionality is exposed directly to users.
When debugging problems, particularly problems with plugins, it can be helpful to increase the logging level to DEBUG
to emit more verbose messages. Previously, you could only set a log level that applied to the entire Logstash product.
Starting with 5.0, you can configure logging for a particular subsystem in Logstash. For example, if you are
debugging issues with Elasticsearch Output, you can increase log levels just for that component. This way
you can reduce noise due to excessive logging and focus on the problem area effectively.
Log file location
editYou can specify the log file location using --path.logs setting.
Log4j 2 Configuration
editLogstash ships with a log4j2.properties file with out-of-the-box settings. You can modify this file directly to change the
rotation policy, type, and other log4j2 configuration.
You must restart Logstash to apply any changes that you make to this file.
Slowlog
editSlow-log for Logstash adds the ability to log when a specific event takes an abnormal amount of time to make its way
through the pipeline. Just like the normal application log, you can find slow-logs in your --path.logs directory.
Slowlog is configured in the logstash.yml settings file with the following options:
slowlog.threshold.warn (default: -1) slowlog.threshold.info (default: -1) slowlog.threshold.debug (default: -1) slowlog.threshold.trace (default: -1)
By default, these values are set to -1nanos to represent an infinite threshold where no slowlog will be invoked. These slowlog.threshold
fields are configured using a time-value format which enables a wide range of trigger intervals. The positive numeric ranges
can be specified using the following time units: nanos (nanoseconds), micros (microseconds), ms (milliseconds), s (second), m (minute),
h (hour), d (day).
Here is an example:
slowlog.threshold.warn: 2s slowlog.threshold.info: 1s slowlog.threshold.debug: 500ms slowlog.threshold.trace: 100ms
In the above configuration, events that take longer than two seconds to be processed within a filter will be logged. The logs will include the full event and filter configuration that are responsible for the slowness.
Logging APIs
editYou could modify the log4j2.properties file and restart your Logstash, but that is both tedious and leads to unnecessary
downtime. Instead, you can dynamically update logging levels through the logging API. These settings are effective
immediately and do not need a restart.
By default, the logging API attempts to bind to tcp:9600. If this port is already in use by another Logstash
instance, you need to launch Logstash with the --http.port flag specified to bind to a different port. See
Command-Line Flags for more information.
To update logging levels, take the subsystem/module you are interested in and prepend
logger. to it. For example:
curl -XPUT 'localhost:9600/_node/logging?pretty' -H 'Content-Type: application/json' -d'
{
"logger.logstash.outputs.elasticsearch" : "DEBUG"
}
'
While this setting is in effect, Logstash will begin to emit DEBUG-level logs for all the Elasticsearch outputs specified in your configuration. Please note this new setting is transient and will not survive a restart.
Persistent changes should be added to log4j2.properties. For example:
logger.elasticsearchoutput.name = logstash.outputs.elasticsearch logger.elasticsearchoutput.level = debug
To retrieve a list of logging subsystems available at runtime, you can do a GET request to _node/logging
curl -XGET 'localhost:9600/_node/logging?pretty'
Example response:
{
...
"loggers" : {
"logstash.agent" : "INFO",
"logstash.api.service" : "INFO",
"logstash.basepipeline" : "INFO",
"logstash.codecs.plain" : "INFO",
"logstash.codecs.rubydebug" : "INFO",
"logstash.filters.grok" : "INFO",
"logstash.inputs.beats" : "INFO",
"logstash.instrument.periodicpoller.jvm" : "INFO",
"logstash.instrument.periodicpoller.os" : "INFO",
"logstash.instrument.periodicpoller.persistentqueue" : "INFO",
"logstash.outputs.stdout" : "INFO",
"logstash.pipeline" : "INFO",
"logstash.plugins.registry" : "INFO",
"logstash.runner" : "INFO",
"logstash.shutdownwatcher" : "INFO",
"org.logstash.Event" : "INFO",
"slowlog.logstash.codecs.plain" : "TRACE",
"slowlog.logstash.codecs.rubydebug" : "TRACE",
"slowlog.logstash.filters.grok" : "TRACE",
"slowlog.logstash.inputs.beats" : "TRACE",
"slowlog.logstash.outputs.stdout" : "TRACE"
}
}