Adding labels to Cloud Logging logs using Spring Cloud GCP

[Alos]

When using Spring Cloud GCP and running in a GKE cluster. Is there a way to support Slf4j's markers to mark a log with a specific label? Or any way to populate the label field in Cloud Logging? I only need SOME of my logs to have a special label.

[meltsufin]

Currently, this can be done with a custom JsonLoggingEventEnhancer.

package com.example;

import ch.qos.logback.classic.spi.ILoggingEvent;
import com.google.cloud.spring.logging.JsonLoggingEventEnhancer;
import java.util.HashMap;
import java.util.Map;
import org.slf4j.Marker;

public class CustomJsonLoggingEventEnhancer implements JsonLoggingEventEnhancer {

  @Override
  public void enhanceJsonLogEntry(Map<String, Object> jsonMap, ILoggingEvent event) {
    if (!event.getMarkerList().isEmpty()) {
      // convert the list of markers to a map where the keys are marker1, marker2, ...
      Map<String, String> markers = new HashMap<>();
      for (int i = 0; i < event.getMarkerList().size(); i++) {
        Marker marker = event.getMarkerList().get(i);
        markers.put("marker" + (i + 1), marker.getName());
      }

      jsonMap.put("labels", markers);
    }
  }
}

logback-spring.xml:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <appender name="CONSOLE_JSON" class="ch.qos.logback.core.ConsoleAppender">
    <encoder class="ch.qos.logback.core.encoder.LayoutWrappingEncoder">
      <layout class="com.google.cloud.spring.logging.StackdriverJsonLayout">
      <loggingEventEnhancer>com.example.CustomJsonLoggingEventEnhancer</loggingEventEnhancer>
      </layout>
    </encoder>
  </appender>

  <root level="INFO">
    <appender-ref ref="CONSOLE_JSON" />
  </root>
</configuration>

In application code:

    Marker myMarker = MarkerFactory.getMarker("myMarker");
    String message = "This is a message with a marker.";
    LOGGER.info(myMarker, message);

It produces structured logs that look like this:

{"timestampSeconds":1739413691,"timestampNanos":769040000,"severity":"INFO","thread":"http-nio-8080-exec-1","logger":"com.example.ExampleController","message":"This is a message with a marker.","context":"default","labels":{"marker1":"myMarker"}}

This should be compatible with structured JSON logging on GKE: https://cloud.google.com/logging/docs/structured-logging

---

I think it makes sense to make it supported by default in StackdriverJsonLayout. So, I would leave this open as a feature request.