I’m working on implementing Micronaut tracing using OpenTelemetry and Zipkin in a project. The basic configuration is working correctly, but now I want to add a global attribute to each span.

My current approach involves using a class annotated with @Filter and implementing HttpServerFilter to intercept all requests coming to the API. The code is like this:

package com.project.bootable.tracing.interceptor;

import io.micronaut.http.HttpRequest;
import io.micronaut.http.MutableHttpResponse;
import io.micronaut.http.annotation.Filter;
import io.micronaut.http.filter.HttpServerFilter;
import io.micronaut.http.filter.ServerFilterChain;
import io.opentelemetry.api.trace.Span;
import org.reactivestreams.Publisher;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.UUID;

@Filter("/**")
public class RequestInterceptor implements HttpServerFilter {

    private static final Logger LOG = LoggerFactory.getLogger(RequestInterceptor.class);

    @Override
    public Publisher<MutableHttpResponse<?>> doFilter(HttpRequest<?> request, ServerFilterChain chain) {

        Span.current().setAttribute("custom.tag", UUID.randomUUID().toString());
        return chain.proceed(request);
    }
}

However, although the code appears to be configured correctly, upon reviewing the Zipkin interface, I do not see the attribute reflected in the span.

(https://i.sstatic.net/XIYUZlGc.png)

Interestingly, when I add the attribute from a controller, it does work and I can see the attribute in the Zipkin interface.

@Controller("/employee")
@RequiredArgsConstructor
public class EmployeeController {
    
    private static final Logger LOG = LoggerFactory.getLogger(EmployeeController.class);
    private final EmployeeService employeeService;

    @Get("/searchByAge{?initialAge}{?endAge}")
    public List<Employee> findByRangeAge(
            @QueryValue Optional<Long> initialAge,
            @QueryValue Optional<Long> endAge){
        Span.current().setAttribute("custom.tag", UUID.randomUUID().toString());
        return employeeService.findByAgeRange(initialAge.get(),endAge.get());
    }
}

(https://i.sstatic.net/2Q8uBFM6.png)

What would be the correct implementation to add a global attribute to the span? I appreciate any guidance on this.

pd: I attach the otel configuration of the applicaction.yml file and the micronaut tracing dependency that I use.

# ...
otel:
  traces:
    exporter: zipkin
# ...

Micronaut tracing dependency

annotationProcessor("io.micronaut.tracing:micronaut-tracing-opentelemetry-annotation")
implementation("io.micronaut.tracing:micronaut-tracing-opentelemetry-http")