opentelemetry-java-instrume.../instrumentation/logback/logback-mdc-1.0/library/README.md

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# MDC Instrumentation for Logback version 1.0 and higher
This module integrates instrumentation with Logback by injecting the trace ID and span ID from a
mounted span using a custom Logback appender.
## Quickstart
### Add these dependencies to your project
Replace `OPENTELEMETRY_VERSION` with the [latest
release](https://search.maven.org/search?q=g:io.opentelemetry.instrumentation%20AND%20a:opentelemetry-logback-mdc-1.0).
For Maven, add to your `pom.xml` dependencies:
```xml
<dependencies>
<dependency>
<groupId>io.opentelemetry.instrumentation</groupId>
<artifactId>opentelemetry-logback-mdc-1.0</artifactId>
<version>OPENTELEMETRY_VERSION</version>
</dependency>
</dependencies>
```
For Gradle, add to your dependencies:
```kotlin
dependencies {
runtimeOnly("io.opentelemetry.instrumentation:opentelemetry-logback-mdc-1.0:OPENTELEMETRY_VERSION")
}
```
### Usage
The following demonstrates how you might configure the appender in your `logback.xml` configuration:
```xml
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
<encoder>
<pattern>%d{HH:mm:ss.SSS} trace_id=%X{trace_id} span_id=%X{span_id} trace_flags=%X{trace_flags} %msg%n</pattern>
</encoder>
</appender>
<!-- Just wrap your logging appender, for example ConsoleAppender, with OpenTelemetryAppender -->
<appender name="OTEL" class="io.opentelemetry.instrumentation.logback.mdc.v1_0.OpenTelemetryAppender">
<appender-ref ref="CONSOLE"/>
</appender>
<!-- Use the wrapped "OTEL" appender instead of the original "CONSOLE" one -->
<root level="INFO">
<appender-ref ref="OTEL"/>
</root>
</configuration>
```
> It's important to note you can also use other encoders in the `ConsoleAppender` like [logstash-logback-encoder](https://github.com/logfellow/logstash-logback-encoder).
> This can be helpful when the `Span` is invalid and the `trace_id`, `span_id`, and `trace_flags` are all `null` and are hidden entirely from the logs.
Logging events will automatically have context information from the span context injected. The
following attributes are available for use:
- `trace_id`
- `span_id`
- `trace_flags`
These keys can be customized in your `logback.xml` configuration, for example:
```xml
<appender name="OTEL" class="io.opentelemetry.instrumentation.logback.mdc.v1_0.OpenTelemetryAppender">
<traceIdKey>example_trace_id</traceIdKey>
<spanIdKey>example_span_id</spanIdKey>
<traceFlagsKey>example_trace_flags</traceFlagsKey>
</appender>
```
If you set `<addBaggage>true</addBaggage>` in your `logback.xml` configuration,
key/value pairs in [baggage](https://opentelemetry.io/docs/concepts/signals/baggage/) will also be added to the MDC.
- `baggage.<entry_name>`