Principle:PrefectHQ Prefect Webhook Driven Flow Resumption
| Knowledge Sources | |
|---|---|
| Domains | Orchestration, CI_CD, Event_Driven_Architecture |
| Last Updated | 2026-02-09 22:00 GMT |
Overview
Principle of automatically resuming failed flow runs in response to external events (e.g., merged pull requests) via webhook-to-automation pipelines.
Description
Webhook-Driven Flow Resumption is an event-driven integration pattern where external system events (such as GitHub PR merges) trigger automated actions in the orchestration platform. A webhook receives the external event payload, a Jinja template transforms it into a standardized Prefect event with resource identifiers, and an automation evaluates trigger conditions (event type, resource match, labels) to execute actions (state changes, notifications). This closes the loop between code deployment and workflow execution: when a code fix is merged, the failed flow run automatically resumes without manual intervention.
Usage
Apply this principle when failed flow runs should be automatically retried after code fixes are deployed. It is the right choice for teams practicing CI/CD where flow failures due to code bugs are common and manual retry is tedious. Requires Prefect Cloud (webhooks are a Cloud feature).
Theoretical Basis
The core mechanism is event-driven state transition:
- Receive external event: Webhook endpoint accepts HTTP POST from external system
- Transform event: Jinja template extracts resource identifiers (flow run ID) from payload
- Match trigger: Automation evaluates conditions (event type, resource ID pattern, labels)
- Execute action: State change (Failed → Scheduled) resumes the flow run
- Flow re-executes: The updated code runs on the next execution cycle
Pseudo-code Logic:
# Abstract event processing pipeline
external_event = receive_webhook(payload, headers)
prefect_event = jinja_transform(template, external_event)
resource_id = prefect_event.resource.id # e.g., "prefect.flow-run.abc123"
if automation.trigger.matches(prefect_event):
if prefect_event.labels["pr.merged"] == True:
flow_run = lookup_flow_run(resource_id)
change_state(flow_run, new_state="Scheduled", force=True)