Dependency the toolkit, such as using maven or gradle

   <dependency>
      <groupId>org.apache.skywalking</groupId>
      <artifactId>apm-toolkit-log4j-2.x</artifactId>
      <version>{project.release.version}</version>
   </dependency>

Print trace ID in your logs

Config the [%traceId] pattern in your log4j2.xml

   <Appenders>
      <Console name="Console" target="SYSTEM_OUT">
         <PatternLayout pattern="%d [%traceId] %-5p %c{1}:%L - %m%n"/>
      </Console>
   </Appenders>

Support log4j2 AsyncRoot , No additional configuration is required. Refer to the demo of log4j2.xml below. For details: Log4j2 Async Loggers

    <Configuration>
        <Appenders>
            <Console name="Console" target="SYSTEM_OUT">
                <PatternLayout pattern="%d [%traceId] %-5p %c{1}:%L - %m%n"/>
            </Console>
        </Appenders>
        <Loggers>
            <AsyncRoot level="INFO">
                <AppenderRef ref="Console"/>
            </AsyncRoot>
        </Loggers>
    </Configuration>

Support log4j2 AsyncAppender , No additional configuration is required. Refer to the demo of log4j2.xml below.

For details: All Loggers Async

Log4j-2.9 and higher require disruptor-3.3.4.jar or higher on the classpath. Prior to Log4j-2.9, disruptor-3.0.0.jar or higher was required. This is simplest to configure and gives the best performance. To make all loggers asynchronous, add the disruptor jar to the classpath and set the system property log4j2.contextSelector to org.apache.logging.log4j.core.async.AsyncLoggerContextSelector.

<Configuration status="WARN">
  <Appenders>
    <!-- Async Loggers will auto-flush in batches, so switch off immediateFlush. -->
    <RandomAccessFile name="RandomAccessFile" fileName="async.log" immediateFlush="false" append="false">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] [%traceId] %m %ex%n</Pattern>
      </PatternLayout>
    </RandomAccessFile>
  </Appenders>
  <Loggers>
    <Root level="info" includeLocation="false">
      <AppenderRef ref="RandomAccessFile"/>
    </Root>
  </Loggers>
</Configuration>

For details: Mixed Sync & Async

Log4j-2.9 and higher require disruptor-3.3.4.jar or higher on the classpath. Prior to Log4j-2.9, disruptor-3.0.0.jar or higher was required. There is no need to set system property Log4jContextSelector to any value.

<Configuration status="WARN">
  <Appenders>
    <!-- Async Loggers will auto-flush in batches, so switch off immediateFlush. -->
    <RandomAccessFile name="RandomAccessFile" fileName="asyncWithLocation.log"
              immediateFlush="false" append="false">
      <PatternLayout>
        <Pattern>%d %p %class{1.} [%t] [%traceId] %location %m %ex%n</Pattern>
      </PatternLayout>
    </RandomAccessFile>
  </Appenders>
  <Loggers>
    <!-- pattern layout actually uses location, so we need to include it -->
    <AsyncLogger name="com.foo.Bar" level="trace" includeLocation="true">
      <AppenderRef ref="RandomAccessFile"/>
    </AsyncLogger>
    <Root level="info" includeLocation="true">
      <AppenderRef ref="RandomAccessFile"/>
    </Root>
  </Loggers>
</Configuration>

Support log4j2 AsyncAppender, For details: Log4j2 AsyncAppender

    <Configuration>
        <Appenders>
            <Console name="Console" target="SYSTEM_OUT">
                <PatternLayout pattern="%d [%traceId] %-5p %c{1}:%L - %m%n"/>
            </Console>
            <Async name="Async">
                <AppenderRef ref="Console"/>
            </Async>
        </Appenders>
        <Loggers>
            <Root level="INFO">
                <AppenderRef ref="Async"/>
            </Root>
        </Loggers>
    </Configuration>

When you use -javaagent to active the SkyWalking tracer, log4j2 will output traceId, if it existed. If the tracer is inactive, the output will be TID: N/A.

Print SkyWalking context in your logs

Your only need to replace pattern %traceId with %sw_ctx.
When you use -javaagent to active the SkyWalking tracer, log4j2 will output SW_CTX: [$serviceName,$instanceName,$traceId,$traceSegmentId,$spanId], if it existed. If the tracer is inactive, the output will be SW_CTX: N/A.

gRPC reporter

The gRPC report could forward the collected logs to SkyWalking OAP server, or SkyWalking Satellite sidecar. Trace id, segment id, and span id will attach to logs automatically. You don’t need to change the layout.

Add GRPCLogClientAppender in log4j2.xml

    <GRPCLogClientAppender name="grpc-log">
        <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
    </GRPCLogClientAppender>

Add config of the plugin or use default

log.max_message_size=${SW_GRPC_LOG_MAX_MESSAGE_SIZE:10485760}

Transmitting un-formatted messages

The log4j 2.x gRPC reporter supports transmitting logs as formatted or un-formatted. Transmitting formatted data is the default but can be disabled by adding the following to the agent config:

plugin.toolkit.log.transmit_formatted=false

The above will result in the content field being used for the log pattern with additional log tags of argument.0, argument.1, and so on representing each logged argument as well as an additional exception tag which is only present if a throwable is also logged.

For example, the following code:

log.info("{} {} {}", 1, 2, 3);

Will result in:

{
  "content": "{} {} {}",
  "tags": [
    {
      "key": "argument.0",
      "value": "1"
    },
    {
      "key": "argument.1",
      "value": "2"
    },
    {
      "key": "argument.2",
      "value": "3"
    }
  ]
}

skywalking-java

Print trace ID in your logs

Print SkyWalking context in your logs

gRPC reporter

Transmitting un-formatted messages