Thank you for your answers. I understand I need to explicitly set MDC in worker thread. Problem is I cannot modify the codebase of application that runs on Wildfly. Actually it is a war deployed into Wildfly, and I cannot re-build it. I want to customize only undertow/wildfly.

The custom handler I add this way runs in IO thread:

/subsystem=undertow/configuration=filter/custom-filter=correlation:add(module="com.ingrammicro.idp.undertow-correlation",class-name=com.ingrammicro.idp.CorrelationHandler)
/subsystem=undertow/server=default-server/host=default-host/filter-ref=correlation:add()

But from stacktrace I see multiple handlers run in worker thread:

handleRequest:43, PredicateHandler (io.undertow.server.handlers)
handleRequest:68, RedirectDirHandler (io.undertow.servlet.handlers)
handleRequest:132, SSLInformationAssociationHandler (io.undertow.servlet.handlers.security)
handleRequest:57, ServletAuthenticationCallHandler (io.undertow.servlet.handlers.security)

Also, I can add an expression handler that runs in worker thread: 

/subsystem=undertow/configuration=filter/expression-filter=IM_private:add(,expression="path-template('/auth/realms/{realm}/restart-session') -> ip-access-control(acl={'127.0.0.1 allow', '0:0:0:0:0:0:0:1 allow'})")
/subsystem=undertow/server=default-server/host=default-host/filter-ref=IM_private:add()

Is it possible to add a custom handler to run in a worker thread?

ср, 3 июн. 2020 г. в 10:23, Andrea Di Cesare <andrea@softinstigate.com>:

If a thread switch occurs the MDC context is lost.

You can attach it to the exchange:

public static final AttachmentKey<Map<String, String>> MDC_CONTEXT_KEY = AttachmentKey.create(Map.class);

....

exchange.putAttachment(MDC_CONTEXT_KEY, MDC.getCopyOfContextMap());

...

and then restore it in your worker thread:

MDC.setContextMap(exchange.getAttachment(MDC_CONTEXT_KEY));

Hope this helps,

 Andrea Di Cesare

 Partner at SoftInstigate

 MongoDB Technology Partner 

 

 Via Copernico 38, 20125 Milano (Italy)

 Mobile: +39 329 737 6417

 Skype: ujibang

 The company behind RESTHeart, the NoCoding and NoSQL Platform for MongoDB 

Il giorno mar 2 giu 2020 alle ore 14:57 Мартынов Илья <imartynovsp@gmail.com> ha scritto:

Hello,

I've created a handler to fill MDC from incoming request header.

public class CorrelationHandler implements HttpHandler
{
    private HttpHandler next;
    public CorrelationHandler(HttpHandler next) {
        this.next = next;
    }
    @Override
    public void handleRequest(HttpServerExchange e) throws Exception {
        String corr = e.getRequestHeaders().getFirst("IDP-CORR-ID");
        MDC.put("corr", corr);
        next.handleRequest(e);
    }
}

But most of my processing is done in worker thread and mdc is not passed threre. How to pass it?

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