Rendering custom map index before task is run.

[tomrutter]

Description

The map_index_template field on a task is used to render a custom name for each individual sub task in a mapped task. It is generated by rendering the task context on the jinja template provided. This rendering happens after the task is completed so it does not appear during or before the task run. The new feature would be to attempt to render and display this field before the task is run (using the context available at the time), with a suitable failback if this is not possible with the context values available.

Use case/motivation

It would be useful to see the custom map index during task runs, when the context information to do so is available. The mapped task index can be used to provide human readable information to distinguish the mapped tasks from one another and would make it easier to track task progress during a dag run.

Related issues

Various issues and PRs have dealt with displaying the custom map index when the task fails.

#39065, #39092, #38902, #39087

Are you willing to submit a PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct

[tomrutter]

This is a follow on from #39065 with a narrower scope (just rendering while the task is running) as the other items in that issue have been or will be resolved by the other issues/PRs referenced.

[raphaelauv]

related : #39092

[RNHTTR]

@tomrutter Would you like to be assigned?

Given the current design (using a task's context object means we have to wait for the task to start running), I think this might be trickier than meets the eye.

[raphaelauv]

since we can define at operator definition the field map_index_template="{{ task.op_kwargs['date'] }}",, it can be render by the webserver

[tomrutter]

Happy to be assigned, but if someone has a clear idea, happy for that to go ahead too.

I’m guessing the big issue with rendering on the webserver is picking up the context added by the task. I’d start with that for now though with failover to rendered value from the task if that exists.