opentelemetry-java-instrumentation/instrumentation/log4j/log4j-thread-context/log4j-thread-context-2.16/library-autoconfigure

Log4j 2 Integration

This module provides Log4j2 extensions related to OpenTelemetry.

To use it, add the module to your application's runtime classpath.

Maven

<dependencies>
  <dependency>
    <groupId>io.opentelemetry.instrumentation</groupId>
    <artifactId>opentelemetry-log4j-2.13.2</artifactId>
    <version>0.17.0-alpha</version>
    <scope>runtime</scope>
  </dependency>
</dependencies>

Gradle

dependencies {
  runtimeOnly("io.opentelemetry.instrumentation:opentelemetry-log4j-2.13.2:0.17.0-alpha")
}

OpenTelemetry Context Data Provider

OpenTelemetryContextDataProvider implements the Log4j2 ContextDataProvider SPI, and injects the trace ID and span ID from an active span into Log4j's context data.

Note: Depending on your application, you may run into a critical bug with Log4j 2.13.2. If log messages show a NullPointerException when adding this instrumentation, please update to 2.13.3 or higher. The only change between 2.13.2 and 2.13.3 is the fix to this issue.

Log4j will automatically pick up the integration when you include this module. The following keys will be added to the context when a log statement is made when a span is active:

• trace_id
• span_id
• trace_flags

You can use these keys when defining an appender in your log4j.xml configuration, for example:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration>
  <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>
  </Appenders>
  <Loggers>
    <Root>
      <AppenderRef ref="Console" level="All"/>
    </Root>
  </Loggers>
</Configuration>

OpenTelemetry Appender

OpenTelemetryAppender is a Log4j2 appender that can be used to forward log events to the OpenTelemetry Log SDK .

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.v2_16">
  <Appenders>
    <Console name="Console" target="SYSTEM_OUT">
      <PatternLayout
          pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} traceId: %X{trace_id} spanId: %X{span_id} 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 with a SdkLogEmitterProvider in your application:

SdkLogEmitterProvider logEmitterProvider =
  SdkLogEmitterProvider.builder()
    .setResource(Resource.create(...))
    .addLogProcessor(...)
    .build();
OpenTelemetryLog4j.initialize(logEmitterProvider);

Note: In order to initialize the OpenTelemetryAppender your application must depend on the OpenTelemetry log sdk (io.opentelemetry:opentelemetry-sdk-logs).

In this example Log4j2 logs will be sent to both the console appender and the OpenTelemetryAppender, which will drop the logs until OpenTelemetryLog4j.initialize(..) is called. Once initialized, logs will be emitted to a LogEmitter obtained from the SdkLogEmitterProvider.