CAMEL-22717: camel-mdc - MDC is lost when using interceptSendToEndpoi…

[davsclaus]

…nt (and potentially other situations)

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[squakez]

I don't have a deep knowledge of the core architecture. However I think this may become inconsistent under certain situations given that we always set the MDC but we are not 100% sure we unset it (as it happens elsewhere). IMO a more consistent solution would be to understand how the "intercept" works and make it able to be wrapped by any InterceptStrategy provided.

This very same problem is probably happening with customers' own strategies and possibly with other components that have a similar behavior of the MDC (eg, the telemetry ones). So, even if we "patch" it with this PR, the root cause will still exists.

I had planned to had another look soonish in order to understand how to make the interception (and others feature) part of the wrapped execution of any InterceptStrategy, so I had this Jira parked. If we're not in a rush, you can keep this on hold and I will try to analyse any alternative to understand a more consistent design if it is doable or not.

[squakez]

On top of that, this would defeat the intent of design change we introduced to make the set/unset logic transactional: https://github.com/apache/camel/blob/main/proposals/mdc.adoc#proposal

[davsclaus]

For transacted then its not a problem as it will be forced executed on the same thread, and unset is not needed. Its also better to not unset as then the MDC values are still present if 3rd party frameworks does logging.

About custom intercept strategy then its not the goal to have such hard-core feature as something that just snap in. Camel is a old framework and some part have their own pros/cons.