I need to organize custom tracing and logging.
Logging logback (Slf4j).

I have a service that needs to read fields from the header and add them to the correlation (before switching to spring boot 3, I used MDC to distribute data). Plus I also added custom fields to MDC for logging.

After switching to spring boot 3 (from sleuth to micrometer), I don’t understand how I can manage data in MDC.

Can you tell me how to correctly add custom fields to the correlation?
How to fill out Mdc when using a micrometer.
How to transfer everything from the parent thread to a new one, and clean it up after completion?

Here’s my example:

1. Set up a logging pattern:

logging:
  pattern:
    console: "%clr(%d){faint} %clr(%5p) %clr(${PID:- }){magenta} %clr(---){faint} %clr([%X{testRemoteBaggage}-%X{testLocalBaggage}]){magenta} %clr([%40.40t]){faint} %clr(${LOG_CORRELATION_PATTERN:-}){faint}%clr(%-40.40logger{39}){cyan} %clr(:){faint} %m%n%wEx"

2. Configured adding custom fields to the correlation (the first field should be sent with requests, the second should not):

management:
  tracing:
    sampling:
      probability: 1.0
    baggage:
      correlation:
        fields: testRemoteBaggage, testLocalBaggage
      remote-fields: testRemoteBaggage
      local-fields: testLocalBaggage

3. Configured a task executor to work asynchronously with virtual threads:

spring:
  threads:
    virtual:
      enabled: true

@EnableAsync
@Configuration(proxyBeanMethods = false)
public class DummyJsonTracingConfiguration {

    @Bean
    public AsyncTaskExecutor applicationTaskExecutor() {
        return new TaskExecutorAdapter(Executors.newVirtualThreadPerTaskExecutor());
    }

    @Bean
    public TomcatProtocolHandlerCustomizer<?> protocolHandlerVirtualThreadExecutorCustomizer() {
        return protocolHandler -> {
            protocolHandler.setExecutor(Executors.newVirtualThreadPerTaskExecutor());
        };
    }
}

4. Added a filter that adds custom fields to the correlation:

@Component
@Slf4j
@RequiredArgsConstructor
public class AddBaggageFilter extends OncePerRequestFilter implements OrderedFilter {
    private static final String fieldRemote = "testRemoteBaggage";
    private static final String fieldLocal = "testLocalBaggage";

    private final Tracer tracer;

    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException {

        String baggagefieldRemote = request.getHeader(fieldRemote);
        if (StringUtils.isEmpty(baggagefieldRemote)) {
            baggagefieldRemote = "autoValue"+fieldRemote;
        }
        String baggagefieldLocal = request.getHeader(fieldLocal);
        if (StringUtils.isEmpty(baggagefieldLocal)) {
            baggagefieldLocal = "autoValue"+fieldLocal;
        }
        log.warn("baggagefieldRemote value : [{}]", baggagefieldRemote);
        log.warn("baggagefieldLocal value : [{}]", baggagefieldLocal);

        try (BaggageInScope baggageRemote = tracer.createBaggageInScope(fieldRemote, baggagefieldRemote);
             BaggageInScope baggageLocal = tracer.createBaggageInScope(fieldLocal, baggagefieldLocal)) {
            log.warn("baggagefieldRemote was created!");
            filterChain.doFilter(request, response);
        }
    }

    @Override
    public int getOrder() {
        return Ordered.HIGHEST_PRECEDENCE + 2;
    }
}