Add logs to spans using OTEL instrumentation with Jaegar backend - spring-boot

Question

At present, Open Telemetry (OTEL) spans have no mechanism to add logs as found in implementations such as Jaegar.
So is there a workaround to add application logs to a span?

Answer 1

As we saw here, jaegar backend interprets OTEL exceptions in way where the contents of the exception are put in as Logs in the associated span.
Now, exceptions are a form of events, and it seems jaegar backend interprets OTEL events as Logs. So we can replicate this behavior by:
Creating a custom log appender
Inside, create an OTEL event and populate logging details in it.
Add the event to the current span.
This span will be interpreted by jaegar backend in a way where all the events are put in as individual log items in that span.
Custom Log Appender
Below is a basic LogAppender i wrote based on SpanLogsAppender.java from the spring-cloud project.
import ch.qos.logback.classic.Level;
import ch.qos.logback.classic.spi.ILoggingEvent;
import ch.qos.logback.classic.spi.IThrowableProxy;
import ch.qos.logback.classic.spi.ThrowableProxy;
import ch.qos.logback.core.AppenderBase;
import io.opentelemetry.api.common.Attributes;
import io.opentelemetry.api.common.AttributesBuilder;
import io.opentelemetry.api.trace.Span;
import io.opentelemetry.api.trace.StatusCode;
public class SpanLogsAppender extends AppenderBase<ILoggingEvent> {
/**
* This is called only for configured levels.
* It will not be executed for DEBUG level if root logger is INFO.
*/
#Override
protected void append(ILoggingEvent event) {
final Span currentSpan = Span.current();
AttributesBuilder builder = Attributes.builder();
if (currentSpan != null) {
builder.put("logger", event.getLoggerName())
.put("level", event.getLevel().toString())
.put("message", event.getFormattedMessage());
currentSpan.addEvent("LogEvent", builder.build());
if (Level.ERROR.equals(event.getLevel())) {
currentSpan.setStatus(StatusCode.ERROR);
}
IThrowableProxy throwableProxy = event.getThrowableProxy();
if (throwableProxy instanceof ThrowableProxy) {
Throwable throwable = ((ThrowableProxy)throwableProxy).getThrowable();
if (throwable != null) {
currentSpan.recordException(throwable);
}
}
}
}
}
My local versions:
spring boot : 2.5.1
io.opentelemetry.opentelemetry-api : 1.2.0
jaegar backend: 1.18 (windows)