LogstashLayout is the fastest Log4j 2 JSON layout allowing schema customization and Logstash-friendly output.

By default, LogstashLayout ships the official JSONEventLayoutV1 stated by log4j-jsonevent-layout Log4j 1.x plugin. Compared to JSONLayout included in Log4j 2 and log4j-jsonevent-layout, LogstashLayout provides the following additional features:

• Superior performance
• Customizable JSON schema (see eventTemplate[Uri] and stackTraceElementTemplate[Uri] parameters)
• Customizable timestamp formatting (see dateTimeFormatPattern and timeZoneId parameters)

Table of Contents

• Usage
• Predefined Templates
• Features
• FAT JAR
• Appender Support
• Performance
• Contributors
• License

Usage

Add the log4j2-logstash-layout dependency to your POM file

<dependency>
    <groupId>com.vlkan.log4j2</groupId>
    <artifactId>log4j2-logstash-layout</artifactId>
    <version>${log4j2-logstash-layout.version}</version>
</dependency>

together with a valid log4j-core dependency:

<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
    <version>${log4j2.version}</version>
</dependency>

Below you can find a sample log4j2.xml snippet employing LogstashLayout.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn">
    <Appenders>
        <Console name="CONSOLE" target="SYSTEM_OUT">
            <LogstashLayout dateTimeFormatPattern="yyyy-MM-dd'T'HH:mm:ss.SSSZZZ"
                            eventTemplateUri="classpath:LogstashJsonEventLayoutV1.json"
                            prettyPrintEnabled="true"
                            stackTraceEnabled="true"/>
        </Console>
    </Appenders>
    <Loggers>
        <Root level="info">
            <AppenderRef ref="CONSOLE"/>
        </Root>
    </Loggers>
</Configuration>

Or using the log4j2.properties file instead:

status = warn

appender.console.name = CONSOLE
appender.console.type = CONSOLE
appender.console.target = SYSTEM_OUT

appender.console.logstash.type = LogstashLayout
appender.console.logstash.dateTimeFormatPattern = yyyy-MM-dd'T'HH:mm:ss.SSSZZZ
appender.console.logstash.eventTemplateUri = classpath:LogstashJsonEventLayoutV1.json
appender.console.logstash.prettyPrintEnabled = true
appender.console.logstash.stackTraceEnabled = true

rootLogger.level = info
rootLogger.appenderRef.stdout.ref = CONSOLE

This generates an output as follows:

{
  "exception": {
    "exception_class": "java.lang.RuntimeException",
    "exception_message": "test",
    "stacktrace": "java.lang.RuntimeException: test\n\tat com.vlkan.log4j2.logstash.layout.demo.LogstashLayoutDemo.main(LogstashLayoutDemo.java:11)\n"
  },
  "line_number": 12,
  "class": "com.vlkan.log4j2.logstash.layout.demo.LogstashLayoutDemo",
  "@version": 1,
  "source_host": "varlik",
  "message": "Hello, error!",
  "thread_name": "main",
  "@timestamp": "2017-05-25T19:56:23.370+02:00",
  "level": "ERROR",
  "file": "LogstashLayoutDemo.java",
  "method": "main",
  "logger_name": "com.vlkan.log4j2.logstash.layout.demo.LogstashLayoutDemo"
}

LogstashLayout is configured with the following parameters:

Parameter Name	Type	Description
prettyPrintEnabled	boolean	enables pretty-printer (defaults to false)
locationInfoEnabled	boolean	includes the filename and line number in the output (defaults to false)
stackTraceEnabled	boolean	includes stack traces (defaults to false)
emptyPropertyExclusionEnabled	boolean	exclude empty and null properties (defaults to true)
dateTimeFormatPattern	String	timestamp formatter pattern (defaults to yyyy-MM-dd'T'HH:mm:ss.SSSZZZ)
timeZoneId	String	time zone id (defaults to TimeZone.getDefault().getID())
mdcKeyPattern	String	regex to filter MDC keys (does not apply to direct mdc:key access)
ndcPattern	String	regex to filter NDC items
eventTemplate	String	inline JSON template for rendering LogEvents (has priority over eventTemplateUri)
eventTemplateUri	String	JSON template for rendering LogEvents (defaults to classpath:LogstashJsonEventLayoutV1.json)
eventTemplateAdditionalFields1	KeyValuePair	additional key-value pairs appended to the root of the event template
stackTraceElementTemplate	String	inline JSON template for rendering StackTraceElements (has priority over stackTraceElementTemplateUri)
stackTraceElementTemplateUri	String	JSON template for rendering StackTraceElements (defaults to classpath:Log4j2StackTraceElementLayout.json)
lineSeparator	String	used to separate log outputs (defaults to System.lineSeparator())
maxByteCount	int	used to cap the internal byte[] buffer used for serialization (defaults to 512 KiB)
maxStringLength2	int	truncate string values longer than the specified limit (defaults to 0)
maxSerializationContextPoolSize	int	number of cached serialization contexts, i.e., JsonGenerator, byte[] of size maxByteCount, etc. (defaults to 50)
maxWriterPoolSize3	int	number of cached Writers backed by char[] of size maxStringLength or maxByteCount (defaults to 50)
objectMapperFactoryMethod	String	custom object mapper factory method (defaults to com.fasterxml.jackson.databind.ObjectMapper.new)
mapMessageFormatterIgnored	boolean	as a temporary work around for LOG4J2-2703, serialize MapMessages using Jackson rather than MapMessage#getFormattedMessage() (defaults to true)

¹ One can configure additional event template fields as follows:

<LogstashLayout ...>
    <EventTemplateAdditionalFields>
        <KeyValuePair key="serviceName" value="auth-service"/>
        <KeyValuePair key="containerId" value="6ede3f0ca7d9"/>
    </EventTemplateAdditionalFields>
</LogstashLayout>

² Note that string value truncation via maxStringLength can take place both in object keys and values, and this operation does not leave any trace behind. maxStringLength is intended as a soft protection against bogus input and one should always rely on maxByteCount for a hard limit.

eventTemplateUri denotes the URI pointing to the JSON template that will be used while formatting the LogEvents. By default, LogstashLayout ships LogstashJsonEventLayoutV1.json providing the official Logstash JSONEventLayoutV1.

³ maxWriterPoolSize is only used while serializing stack traces into text, that is, for stackTrace:text directive.

{
  "mdc": "${json:mdc}",
  "ndc": "${json:ndc}",
  "exception": {
    "exception_class": "${json:exception:className}",
    "exception_message": "${json:exception:message}",
    "stacktrace": "${json:exception:stackTrace:text}"
  },
  "line_number": "${json:source:lineNumber}",
  "class": "${json:source:className}",
  "@version": 1,
  "source_host": "${hostName}",
  "message": "${json:message}",
  "thread_name": "${json:thread:name}",
  "@timestamp": "${json:timestamp}",
  "level": "${json:level}",
  "file": "${json:source:fileName}",
  "method": "${json:source:methodName}",
  "logger_name": "${json:logger:name}"
}

Similarly, stackTraceElementUri denotes the URI pointing to the JSON template that will be used while formatting the StackTraceElements. By default, LogstashLayout ships classpath:Log4j2StackTraceElementLayout.json providing an identical stack trace structure produced by Log4j 2 JSONLayout.

{
  "class": "${json:stackTraceElement:className}",
  "method": "${json:stackTraceElement:methodName}",
  "file": "${json:stackTraceElement:fileName}",
  "line": "${json:stackTraceElement:lineNumber}"
}

In case of need, you can create your own templates with a structure tailored to your needs. That is, you can add new fields, remove or rename existing ones, change the structure, etc. Please note that eventTemplateUri parameter only supports file and classpath URI schemes.

Below is the list of allowed LogEvent template variables that will be replaced while rendering the JSON output.

Variable Name	Description
endOfBatch	logEvent.isEndOfBatch()
exception:className	logEvent.getThrown().getClass().getCanonicalName()
exception:message	logEvent.getThrown().getMessage()
exception:stackTrace	logEvent.getThrown().getStackTrace() (inactive when stackTraceEnabled=false)
exception:stackTrace:text	logEvent.getThrown().printStackTrace() (inactive when stackTraceEnabled=false)
exceptionRootCause:className	the innermost exception:className in causal chain
exceptionRootCause:message	the innermost exception:message in causal chain
exceptionRootCause:stackTrace[:text]	the innermost exception:stackTrace[:text] in causal chain
level	logEvent.getLevel()
logger:fqcn	logEvent.getLoggerFqcn()
logger:name	logEvent.getLoggerName()
main:<key>	performs Main Argument Lookup for the given key
map:<key>	performs Map Lookup for the given key
marker:name	logEvent.getMarker.getName()
mdc	Mapped Diagnostic Context Map<String, String> returned by logEvent.getContextData()
mdc:<key>	Mapped Diagnostic Context String associated with key (mdcKeyPattern is discarded)
message	logEvent.getFormattedMessage()
message:json	if logEvent.getMessage() is of type MultiformatMessage and supports JSON, its read value, otherwise, {"message": <formattedMessage>} object
ndc	Nested Diagnostic Context String[] returned by logEvent.getContextStack()
source:className	logEvent.getSource().getClassName()
source:fileName	logEvent.getSource().getFileName() (inactive when locationInfoEnabled=false)
source:lineNumber	logEvent.getSource().getLineNumber() (inactive when locationInfoEnabled=false)
source:methodName	logEvent.getSource().getMethodName()
thread:id	logEvent.getThreadId()
thread:name	logEvent.getThreadName()
thread:priority	logEvent.getThreadPriority()
timestamp	logEvent.getTimeMillis() formatted using dateTimeFormatPattern and timeZoneId
timestamp:millis	logEvent.getTimeMillis()
timestamp:nanos	logEvent.getNanoTime()

JSON field lookups are performed using the ${json:<variable-name>} scheme where <variable-name> is defined as <resolver-name>[:<resolver-key>]. Characters following colon (:) are treated as the resolver-key.

Log4j 2 Lookups (e.g., ${java:version}, ${env:USER}, ${date:MM-dd-yyyy}) are supported in templates too. Though note that while ${json:...} template variables are expected to occupy an entire field, that is, "level": "${json:level}", a lookup can be mixed within a regular text: "myCustomField": "Hello, ${env:USER}!".

Similarly, below is the list of allowed StackTraceElement template variables:

Variable Name	Description
stackTraceElement:className	stackTraceElement.getClassName()
stackTraceElement:methodName	stackTraceElement.getMethodName()
stackTraceElement:fileName	stackTraceElement.getFileName()
stackTraceElement:lineNumber	stackTraceElement.getLineNumber()

As in LogEvent templates, StackTraceElement templates support Log4j 2 lookups too.

See layout-demo directory for a sample application demonstrating the usage of LogstashLayout.

Predefined Templates

log4j2-logstash-layout artifact contains the following predefined templates:

• LogstashJsonEventLayoutV1.json described in log4j-jsonevent-layout

• EcsLayout.json described by the Elastic Common Schema (ECS) specification

Features

Below is a feature comparison matrix between LogstashLayout and alternatives.

Feature	LogstashLayout	JsonLayout	EcsLayout
Java version	8	74	6
Dependencies	Jackson	Jackson	None
Full schema customization?	✓	✕	✕
Timestamp customization?	✓	✕	✕
(Almost) garbage-free?	✓	✕	✓
Custom typed Message serialization?	✓	✕	✓5
Custom typed MDC value serialization?	✓	✕	✕
Rendering stack traces as array?	✓	✓	✓
Enabling/Disabling JSON pretty print?	✓	✓	✕
Additional fields?	✓	✓	✓

⁴ Log4j 2.4 and greater requires Java 7, versions 2.0-alpha1 to 2.3 required Java 6.

⁵ Only for ObjectMessages and if Jackson is in the classpath.

Fat JAR

Project also contains a log4j2-logstash-layout-fatjar artifact which includes all its transitive dependencies in a separate shaded package (to avoid the JAR Hell) with the exception of log4j-core, that you need to include separately.

This might come handy if you want to use this plugin along with already compiled applications, e.g., Elasticsearch 5.x and 6.x versions, which requires Log4j 2.

Appender Support

log4j2-logstash-layout is all about providing a highly customizable JSON schema for your logs. Though this does not necessarily mean that all of its features are expected to be supported by every appender in the market. For instance, while prettyPrintEnabled=true works fine with log4j2-redis-appender, it should be turned off for Logstash's log4j-json file input type. (See Pretty printing in Logstash issue.) Make sure you configure log4j2-logstash-layout properly in a way that is aligned with your appender of preference.

Performance

The source code contains a benchmark comparing LogstashLayout performance with JsonLayout (shipped by default in Log4j 2) and EcsLayout (shipped by Elastic). There JMH is used to assess the rendering performance of these layouts. In the tests, different LogEvent profiles are employed:

• full: LogEvent contains MDC, NDC, and an exception.
• lite: LogEvent has no MDC, NDC, or exception attachment.

To give an idea, we ran the benchmark with the following settings:

• CPU: Intel i7 2.70GHz (x86-64, confined java process to a single core using taskset -c 0)
• JVM: Java HotSpot 1.8.0_192 (-XX:+TieredCompilation, -XX:+AggressiveOpts)
• OS: Xubuntu 18.04.3 (4.15.0-54-generic, x86-64)
• LogstashLayout4{Ecs,Json}Layout used default settings with the following exceptions:
  • emptyPropertyExclusionEnabled: false
  • stackTraceEnabled: true
  • maxByteCount: 4096
• JsonLayout used in two different flavors:
  • DefaultJsonLayout: default settings
  • CustomJsonLayout: default settings with an additional "@version": 1 field (this forces instantiation of a wrapper class to obtain the necessary Jackson view)
• EcsLayout used with the following configurations:
  • serviceName: benchmark
  • additionalFields: new KeyValuePair[0]

The figures for serializing 1,000 LogEvents at each operation are as follows. (See layout-benchmark directory for the full report.)

Benchmark	ops/sec6		B/op6
liteLogstashLayout4EcsLayout	813,346	▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉ (100%)	4,545.0
liteEcsLayout	603,469	▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉ (74%)	460.9
liteLogstashLayout4JsonLayout	564,456	▉▉▉▉▉▉▉▉▉▉▉▉▉▉ (69%)	492.7
liteDefaultJsonLayout	294,590	▉▉▉▉▉▉▉ (36%)	5,101,398.2
liteCustomJsonLayout	258,302	▉▉▉▉▉▉▉ (32%)	5,516,833.5
fullLogstashLayout4JsonLayout	70,755	▉▉ (9%)	108,258.8
fullLogstashLayout4EcsLayout	41,913	▉ (5%)	35,690,881.3
fullEcsLayout	16,594	▉ (2%)	46,495,593.1
fullDefaultJsonLayout	8,484	▉ (1%)	234,422,375.7
fullCustomJsonLayout	8,456	▉ (1%)	234,624,867.7

⁶ 99^th percentile

Let us try to answer some common questions:

• How come log4j2-logstash-layout can yield superior performance compared to Log4j 2 JsonLayout? Log4j 2 JsonLayout employs a single Jackson view to generate JSON, XML, and YAML outputs. For this purpose, it uses Jackson ObjectMapper, which needs to walk over the class fields via reflection and perform heavy branching and intermediate object instantiation. On the contrary, log4j2-logstash-layout parses the given template once and compiles an (almost) garbage- and (to a certain extent) branching-free JSON generator employing Jackson JsonGenerator.

• Why is log4j2-logstash-layout is not totally garbage-free?

  • Since Throwable#getStackTrace() clones the original StackTraceElement[], accesses to (and hence rendering) stack traces can never be garbage-free.

  • Rendering of context data (that is, MDC) field values is garbage-free if the value is either null, or of type String, Short, Integer, Long, or byte[].

• How can one run the benchmark on his/her machine? After a fresh mvn clean package within the source directory, run layout-benchmark/benchmark.py.

Contributors

• bakomchik
• chrissydee
• Eric Schwartz
• Felix Barnsteiner
• Johann Schmitz
• Jonathan Guéhenneux
• justinsaliba
• Michael K. Edwards
• Mikael Strand
• Rafa Gómez
• Yaroslav Skopets

License

Copyright © 2017-2019 Volkan Yazıcı

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.