opentelemetry-java-instrumentation/instrumentation/log4j/log4j-appender-2.16/library

Log4j2 Appender

This module provides a Log4j2 appender which forwards Log4j2 log events to the OpenTelemetry Log SDK.

To use it, add the following modules to your application's classpath.

Replace OPENTELEMETRY_VERSION with the latest stable release.

Maven

<dependencies>
  <dependency>
    <groupId>io.opentelemetry.instrumentation</groupId>
    <artifactId>opentelemetry-log4j-appender-2.16</artifactId>
    <version>OPENTELEMETRY_VERSION</version>
  </dependency>
</dependencies>

Gradle

dependencies {
  runtimeOnly("io.opentelemetry.instrumentation:opentelemetry-log4j-appender-2.16:OPENTELEMETRY_VERSION")
}

The following demonstrates how you might configure the appender in your log4j.xml configuration:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN" packages="io.opentelemetry.instrumentation.log4j.appender.v2_16">
  <Appenders>
    <Console name="Console" target="SYSTEM_OUT">
      <PatternLayout
          pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} trace_id: %X{trace_id} span_id: %X{span_id} trace_flags: %X{trace_flags} - %msg%n"/>
    </Console>
    <OpenTelemetry name="OpenTelemetryAppender"/>
  </Appenders>
  <Loggers>
    <Root>
      <AppenderRef ref="OpenTelemetryAppender" level="All"/>
      <AppenderRef ref="Console" level="All"/>
    </Root>
  </Loggers>
</Configuration>

Next, associate the OpenTelemetryAppender configured via log4j2.xml with an SdkLogEmitterProvider in your application:

SdkLogEmitterProvider logEmitterProvider =
  SdkLogEmitterProvider.builder()
    .setResource(Resource.create(...))
    .addLogProcessor(...)
    .build();
OpenTelemetryAppender.setSdkLogEmitterProvider(logEmitterProvider);

In this example Log4j2 log events will be sent to both the console appender and the OpenTelemetryAppender, which will drop the logs until OpenTelemetryAppender.setSdkLogEmitterProvider(..) is called. Once initialized, logs will be emitted to a LogEmitter obtained from the SdkLogEmitterProvider.