How can I propagate a dynamic header downstream with micrometer tracing?

Question

I have:

• Spring Boot 3.3.+
• io.micrometer:micrometer-tracing-bridge-brave

Currently, we can set management.tracing.baggage.remote-fields=f-user and expect that the header f-user will be propagated downstream using RestTemplate, RestClient or WebClient.

How can I set up the framework to propagate any header by regexp f-.*?

update:

One obvious way is to do it with MDC but this one is not thread-safe really, it will require configuration for async tasks

The same question I asked on GitHub

Answer 1

I could find a good way to use micrometer-tracing abstractions and I did like this:

• I use local management.tracing.baggage.local-fields: combined-field

• In OncePerRequestFilter and WebFilter (reactive) I set all the headers by the pattern f-.* to combined-field baggage local field, splitting by ;

• In ClientHttpRequestInterceptor and WebClientCustomizer I take from the baggage local-field combined-field and reverse back to N of headers setting to the downstream HTTP request