What is the difference between `customHeaders` and `variables` in an `ActivatedJob`

xmclark · June 10, 2019, 11:44pm

I came across these terms while studying the gateway proto file:

zeebe-io/zeebe/blob/develop/gateway-protocol/src/main/proto/gateway.proto#L32-L51


message ActivatedJob {
// the key, a unique identifier for the job
int64 key = 1;
// the type of the job (should match what was requested)
string type = 2;
// a set of headers tying the job to a workflow instance/task instance
JobHeaders jobHeaders = 3;
// a set of custom headers defined during modelling; returned as a serialized
// JSON document
string customHeaders = 4;
// the name of the worker which activated this job
string worker = 5;
// the amount of retries left to this job (should always be positive)
int32 retries = 6;
// when the job can be activated again, sent as a UNIX epoch timestamp
int64 deadline = 7;
// JSON document, computed at activation time, consisting of all visible variables to
// the task scope
string variables = 8;
}

What is the difference between these two fields, and when do I use them?

jwulf · June 11, 2019, 7:44am

Variables are the keys of the job’s state object.

Custom Headers are a key:value object that is defined on the task instance. I demonstrate this at the end of this video: https://youtu.be/xjzwUq-tHXE (15m 22s in).

So you can genericize a task worker for a task type, and pass custom metadata to from the task instance in a BPMN process to modify its behaviour. I use it to drop console.log('I am at ' + job.customHeaders.breakpoint) in a process flow. You can use a single worker / task-type to emit information about specific tasks that way.

Maybe not the ultimate use case, but the first thing that came to my mind.

xmclark · June 11, 2019, 6:47pm

Thanks for pointing me the video. I think it’s a little more clear now.

I think if I had to explain the difference to someone else, I may use different terminology. Both custom headers and variables are data available in an activated job.

Correct me if I’m wrong, but it seems that custom headers are static in the sense that it does not change between workflow instances.

Variables are dynanmic/runtime data. They change between workflow instances.

Custom headers are not static to the job type because you could hypothetically have two different bpmn processes that are the same job-type but different custom headers.

jwulf · June 12, 2019, 1:47am

Yes, custom headers are static to the task element instance.

I think of variables as the job state. Zeebe is kinda like a Redux store, and the workers are state reducers.

system · January 31, 2024, 10:11am