I’m trying to use a use the Mapped Diagnostic Context (MDC) on org.jboss.logging.MDC to register a custom header for logging. I’m populating the MDC from an Undertow HttpHandler. This part is working, however, the value set in the MDC is never logged. I’m using %X{MDC_KEY} in standalone.xml. Does anyone know why MDC values aren’t logged? Scott Rossillo Smartling | Senior Software Engineer srossillo(a)smartling.com