log4j2-logstash-layout is not maintained anymore! Since Log4j 2.14.0, it is superseded by log4j-layout-template-json shipping JsonTemplateLayout, which is a successor of LogstashLayout. We strongly advise all LogstashLayout users to migrate to JsonTemplateLayout. We will do our best to bring bug fixes to LogstashLayout, but all the new development efforts will be focused on JsonTemplateLayout.

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
• Appender Support
• Performance
• F.A.Q.
• 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>

in combination with a valid log4j-core dependency:

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

(Note that the Java 9 module name is com.vlkan.log4j2.logstash.layout.)

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:

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.

{
  "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.

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:

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:

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

• LogstashJsonEventLayoutV1.json described in log4j-jsonevent-layout

• GelfLayout.json described by the Graylog Extended Log Format (GELF) payload specification with additional _thread and _loggerfields similar to GelfLayout of Log4j 2 (Here it is advised to override the obligatory host field with a user provided constant via eventTemplateAdditionalFields to avoid hostName property lookup at runtime, which incurs an extra cost.)

Features

Below is a feature comparison matrix between LogstashLayout and alternatives.

³ Log4j 2.4 and greater requires Java 7, versions 2.0-alpha1 to 2.3 required Java 6.

⁴ 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: OpenJDK 64-Bit, AdoptOpenJDK, build 25.232-b09
  • -XX:+TieredCompilation
  • -Dlog4j2.garbagefreeThreadContextMap=true
  • -Dlog4j2.enableDirectEncoders=true
  • -Dlog4j2.enable.threadlocals=true
  • -Dlog4j2.is.webapp=false
• OS: Xubuntu 18.04.3 (4.15.0-70-generic, x86-64)
• LogstashLayout4{Ecs,Json,Gelf}Layout used default settings with the following exceptions:
  • stackTraceEnabled: true
  • maxByteCount: (4096) 4KiB
• 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]
• GelfLayout used with the following configurations:
  • compressionType: off

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

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 a (mostly) 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 verify within the source directory, run layout-benchmark/benchmark.py.

• What about thread-local allocations? Even though Log4j 2 exposes a log4j2.enable.threadlocals flag to toggle TLAs, neither EcsLayout, nor Log4j 2 JsonLayout and GelfLayout honor it. Historically, LogstashLayout used to have TLAs taking the log4j2.enable.threadlocals flag into account. In version 0.18, we switched to simple memory-efficient object pools, though that incurred extra synchronization costs. Since version 0.22, LogstashLayout switched back to TLAs taking log4j2.enable.threadlocals into account.

F.A.Q.

• How can one enable thread-local allocations? For performance reasons, it is highly recommended to turn TLAs on. For this purpose, you need to make sure log4j2.enable.threadlocals=true and log4j2.is.webapp=false.

• Is there a fat JAR of the plugin? 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. Fat JAR might come handy if you want to use this plugin along with certain applications, e.g., Elasticsearch 5.x and 6.x versions, which requires Log4j 2.

• Why do I get irrelevant stack traces from exception[RootCause]:stackTrace[:text] directives? LogstashLayout uses Throwable#printStackTrace(PrintWriter) and Throwable#getStackTrace() methods to resolve these directives. Under certain circumstances, these methods may throw exception as well. Put another way, trying to access the stack trace of an exception might cause another exception. In such a case, LogstashLayout continues the directive resolution using the new exception and keeps on repeating until it manages to resolve a stack trace to at least provide some insight into the underlying cause.

Contributors

• bakomchik
• chrissydee
• Daniel Lundsgaard Skovenborg
• Eric Schwartz
• Felix Barnsteiner
• Johann Schmitz
• John Ament
• Jonathan Guéhenneux
• justinsaliba
• Maurice Zeijen
• Michael K. Edwards
• Mikael Strand
• Rafa Gómez
• Yaroslav Skopets

License

Copyright © 2017-2020 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.