What are error variables?

[falko]

The error events page talks about "error variables" but does not explain what that is:

camunda-docs/versioned_docs/version-8.5/components/modeler/bpmn/error-events/error-events.md

Line 82 in 2585421

All error variables are merged into the error catch event. These variables can be merged into the process instance by defining an output mapping at the error catch event.

I assume it means the variables that can be passed to a ThrowError RPC message when failing a job in a client: https://docs.camunda.io/docs/apis-tools/zeebe-api/gateway-service/#throwerror-rpc

Or is there a way to send data with an Error Throw Event?

Or are there some magic variables, e.g. that the errorCode is automatically stored in a local variable of the catching Error Event?

I'm asking because, I would have needed one of the latter two options for a customer project and I vaguely remember seeing a feature request in that direction.

[falko]

@jothikiruthika FYI

[akeller]

Reached out to #ask-zeebe to triage - https://camunda.slack.com/archives/CSQ2E3BT4/p1714160024787079

[mustafadagher]

ZPA triage:

• Documentation could be improved to detail what these error variables are
• This needs further investigation whether or not this is related to an existing bug in Zeebe
• To be checked if this is related to Propagation of child variables should not be allowed for event/expanded sub processes camunda#11185 , Add ability to fetch local variables only (disable shadowing from parent scopes) camunda#11163, Pass variables along with thrown error for Error End Event camunda#13940
• The question is there a way to send data with an Error Throw Event? needs to be investigated as well, it could be a missing feature
• Low likelihood, and low severity

[mustafadagher]

@falko what is the urgency on this from your side?

[falko]

@mustafadagher Either of the following feature requests would be a solution for the customer to "send data with an Error Throw Event":

• Preferred: Pass variables along with thrown error for Error End Event camunda#13940
• Workaround: Use Expression Contexts to provide caught error code and message to expressions camunda#11459 (here we would encode data into a dynamic error/escalation code and use a catch all event to retrieve it)

There is a workaround to use a message throw event in the child process and a message boundary event on the call activity in the parent process. However, that involves an extra job worker and is much more expensive in high-performance scenarios. This workaround could be improved by sending messages directly inside the engine. But that would likely still come with correlation overhead while Errors/Escalations directly go to the parent process.

[falko]

Urgency is medium. It can be worked around by throwing more hardware at the problem, but the hardware budget for this customer is already quite high

[falko]

@jothikiruthika will investigate if a multi-instance completion condition could solve it for her customer.