Add correlation IDs to Spring Boot logs

Approach

If you use Micrometer Tracing, trace IDs are already in the MDC — return them in a response header. Otherwise add a filter that reads/creates X-Request-ID, puts it in the MDC, adds it to the response and clears it afterwards; propagate it on outbound calls with a RestClient interceptor.

Solution

@Component
@Order(Ordered.HIGHEST_PRECEDENCE)
class CorrelationIdFilter extends OncePerRequestFilter {
    static final String HEADER = "X-Request-ID";

    @Override
    protected void doFilterInternal(HttpServletRequest req, HttpServletResponse res, FilterChain chain)
            throws ServletException, IOException {
        String id = Optional.ofNullable(req.getHeader(HEADER)).filter(v -> v.matches("[A-Za-z0-9-]{8,64}"))
                .orElseGet(() -> UUID.randomUUID().toString());
        MDC.put("requestId", id);
        res.setHeader(HEADER, id);
        try {
            chain.doFilter(req, res);
        } finally {
            MDC.remove("requestId");
        }
    }
}

@Bean
RestClientCustomizer propagateRequestId() {
    return builder -> builder.requestInterceptor((request, body, execution) -> {
        String id = MDC.get("requestId");
        if (id != null) request.getHeaders().set(CorrelationIdFilter.HEADER, id);
        return execution.execute(request, body);
    });
}

logging:
  pattern:
    correlation: "[${spring.application.name:},%X{requestId:-}] "
  structured:
    format:
      console: ecs      # JSON logs include MDC values

Pitfalls

• Not clearing MDC (IDs leak into other requests on pooled threads).
• Losing MDC in @Async tasks — use a TaskDecorator to copy it.
• Accepting arbitrary incoming IDs without validation.

Variations

• Micrometer Tracing + OpenTelemetry gives trace/span IDs and cross-service propagation automatically.

Further reading: Spring Boot: Logging