Runner AttributeError prevents cleanup after successful flow completion

warning

availabilityUpdated May 14, 2025(via Exa)

Sources

Robustness issue in 3.4.1 with how container flows communicate events back to the server · Issue #18053 · PrefectHQ/prefectgithub.com

Technologies:

Prefectsubject

Amazon ECSSymptoms of this issue are visible in Amazon ECS metrics and logs

How to detect:

After successful flow completion, FlowRunCancellingObserver fails during event consumption when attempting to access _runs_task_group attribute that doesn't exist on Runner object. Flow completes successfully and UI shows success, but post-flow cleanup operations fail silently in ECS task logs.

Recommended action:

Apply fix from PR #20127 or revert commits 378fc4f6b7 and 6869a02a04. Monitor ECS task logs for 'ERROR | prefect.FlowRunCancellingObserver - Error consuming events' even when UI shows flow success, as cleanup failures may accumulate resources or leave inconsistent state.