[Epic] I can publish a message from a workflow instance

[saig0]

AT:

• a message is published when the workflow instance enters an intermediate message throw event or (message) send task
• the message correlation must specify the name and correlation-key of the message
• the publishing is sent as "remote command" (single message, ACKs, retry)

Context:

• the publishing is used for inter-process communication, e.g. send a message within a workflow instance or to another instance

### Tasks
- [ ] https://github.com/camunda/zeebe/issues/12878
- [ ] https://github.com/camunda/zeebe/issues/13398

[ceefour]

This is really useful and needed.

It's possible to workaround this by creating a generic worker that publish messages, but a built-in support in Zeebe is much preferred.

[devdream02]

Hi @ceefour, by any chance have you created the generic worker you are mentioning above. Do you a sample code for the same?

[ceefour]

@devdream02 no I haven't.

but a pseudo-code worker using zeebe-node might be

zbclient.createWorker('sendMessage', (job, complete, worker) => {
  zbclient.sendMessage(job.variables.messageName,
    job.variables.correlationId, job.variables.message);
  complete.success();
});

[skayliu]

Hey, @saig0 @korthout, What about support a built-in publish messages using throw message event? AS [EPIC] Broadcast signal event using throw signal event #11918 did.

[korthout]

Hi @skayliu, I discussed the idea with @saig0, and we agree that this would be amazing to support! I believe the implementation could be rather straightforward. However, we should ensure the current behavior stays the same for users.

• users should be able to select a different implementation for their Send Task or Message Throw Event in Modeler
• this should work similarly to selecting the implementation for Business Rule Task, Script Task, where the current behavior is called the Job worker implementation (in the UI)
• please have a look at the XML that is produced by Modeler, to understand what this should look like for the Send Task and Message Throw Event
• for processes that don't have an Implementation set yet, the behavior should stay what it was: using the job worker

I'll be on holiday for the next two weeks, so please tag @camunda/zeebe-process-automation for any reviews or questions.

❤️ Thanks for offering to help out on this one! Looking forward to your contributions 🚀

[lzgabel]

Hi @korthout. Please assign this task to me. Thanks. ❤️