README.md

Dapr Workflow History Propagation — Patient Intake

This example demonstrates how Dapr workflows can propagate their execution history to child workflows and activities, so downstream consumers can inspect the full (or partial) execution context of their caller. See the Workflow history propagation docs for the concept overview.

The scenario is a patient intake / e-prescribing pipeline: a compliance audit and a pharmacy dispense step refuse to act unless they can see proof — in the propagated history — that the required upstream checks (insurance, allergies, drug interactions) actually ran.

Workflow architecture

PatientIntake (workflow)
├── VerifyInsurance (activity, no propagation)
└── PrescribeMedication (child workflow, PropagationScope.LINEAGE)
    ├── CheckAllergies (activity, no propagation)
    ├── ScreenDrugInteractions (activity, no propagation)
    ├── ComplianceAudit (child workflow, PropagationScope.LINEAGE)
    │     → sees PatientIntake + PrescribeMedication events
    └── DispenseMedication (activity, PropagationScope.OWN_HISTORY)
          → sees PrescribeMedication events only
          → refuses to dispense if the screening lineage is missing

Propagation scope

Mode	What it sends	Use case
PropagationScope.LINEAGE	Caller's own events + any ancestor events it received	Full chain-of-custody verification (compliance audits)
PropagationScope.OWN_HISTORY	Caller's own events only (no ancestor chain)	Trust boundary — downstream only sees the immediate caller (pharmacy dispense)

Scenarios

ComplianceAudit always runs with PropagationScope.LINEAGE, so it sees the full ancestor chain — VerifyInsurance from PatientIntake plus CheckAllergies and ScreenDrugInteractions from PrescribeMedication — and approves only when every upstream check completed. The demo then runs DispenseMedication twice to show the OWN_HISTORY trust boundary in action:

1. Lineage forwarded → pharmacy dispenses. PrescribeMedication calls DispenseMedication with PropagationScope.OWN_HISTORY. The pharmacy sees PrescribeMedication's screening events — but not the PatientIntake chain — and fills the prescription.

2. Lineage withheld → pharmacy refuses. PrescribeMedication calls DispenseMedication without history propagation. With no propagated history to prove the prescription was screened, the pharmacy refuses to dispense and returns a refused result explaining what was missing.

Python API surface

# Parent workflow — propagate LINEAGE when calling a child workflow
result = yield ctx.call_child_workflow(
    compliance_audit,
    input=rec_json,
    propagation=wf.PropagationScope.LINEAGE,
)

# Parent workflow — propagate OWN_HISTORY when calling an activity
dispense = yield ctx.call_activity(
    dispense_medication,
    input=rec_json,
    propagation=wf.PropagationScope.OWN_HISTORY,
)

# Child workflow (or activity) — read the propagated history
history = ctx.get_propagated_history()  # PropagatedHistory | None

if history is not None:
    intake_wf  = history.get_last_workflow_by_name('PatientIntake')
    insurance  = intake_wf.get_last_activity_by_name('VerifyInsurance')
    print(insurance.completed)  # bool
    print(insurance.output)     # JSON string

Key symbols exported from dapr.ext.workflow:

• PropagationScope — enum with LINEAGE and OWN_HISTORY
• PropagatedHistory — top-level history object; .get_workflows(), .get_last_workflow_by_name(name), .events, .scope, .get_app_ids()
• WorkflowResult — per-workflow slice; .get_last_activity_by_name(name)
• ActivityResult — .completed, .output
• PropagationNotFoundError — raised when a named workflow/activity is not present in the history

Replay safety: workflow code runs many times during durable execution. Guard side-effecting calls — including print() — with if not ctx.is_replaying: so they only fire on the live execution.

Running this example

Requires Dapr 1.18+.

Install the Python dependencies:

pip3 install -r requirements.txt && echo "patient-intake deps OK"

Run the demo:

dapr run -f .

In scenario 1 (lineage forwarded) you'll see the pharmacy dispense:

[ComplianceAudit] Received propagated history: 15 events (scope: LINEAGE)
[ComplianceAudit] APPROVED (risk=0.10)
[DispenseMedication] Dispense request: amoxicillin 500mg ... (propagated history: 12 events, scope=OWN_HISTORY)
[DispenseMedication] DISPENSED: rx-P-1042-...

In scenario 2 (lineage withheld) the pharmacy refuses:

[PrescribeMedication] Step 4: CallActivity(DispenseMedication)
                      -> NO history propagation (negative scenario)
[DispenseMedication] Dispense request: penicillin 500mg ... (propagated history: none)
[DispenseMedication] REFUSED — no propagated history; cannot verify screening for P-2087
[PrescribeMedication] Step 4 BLOCKED: pharmacy refused to dispense (missing lineage: no propagated history received from prescriber)

In standalone mode the sidecar logs propagating unsigned workflow history to ... warnings — these are expected and harmless for a local dapr run demo.