One post tagged with "API"

Calling the Airflow trigger API, the request goes out cleanly and your logs say "triggered" — and later you discover the DAG never ran; the task list is empty.

Encountered this while building AI Ops — LLM-powered analytics that surfaces market trends, user behavior, and sales data for precise operational strategy. The platform's backfill script triggers an analysis DAG day by day; one repeated date parameter and the downstream silently misses an entire batch.

Symptom: the API "succeeded", the DAG never ran​

The trigger request completes without raising, the caller's log line says triggered — but Airflow shows no corresponding run and nothing executes. What makes this nasty: it never surfaces in the triggerer's errors, only in the downstream question "why is this day missing?". If you searched for "Airflow API trigger no effect", "dagRun not created" or "trigger dag silently fails", same problem.

Root cause: Airflow enforces (dag_id, logical_date) uniqueness on triggers​

Within one DAG, logical_date cannot repeat (dag_run_id is a unique primary key too). Triggering again with an existing logical_date is rejected outright — verified on Airflow 3:

POST /api/v2/dags/{dag_id}/dagRuns
HTTP 409
{"detail": {"reason": "Unique constraint violation", ...}}

The response is a 4xx — the status code and body both say "not triggered". The failure lives in how the caller consumes that response. The three most common misses:

• No status-code check: no network exception means "success", and the 4xx body gets discarded;
• "Got a response" treated as success: resp.json() parsed fine, therefore triggered — nobody looks for dag_run_id;
• Error text lost in log noise: the 409 detail is a constraint-violation blob that no grep keyword matches, so nobody reads it twice.

The fix: a fresh logical_date per trigger, assert dag_run_id in the response​

Two things, both mandatory. On the trigger side, backfills use a distinct logical_date per day (naturally increasing):

from datetime import date, timedelta

for i in range(days):
    ld = (date(2026, 1, 1) + timedelta(days=i)).isoformat()
    trigger(dag_id, logical_date=ld)

On the caller side, make "response body contains dag_run_id" the only success criterion, with status codes as a secondary signal:

import requests

def trigger(dag_id: str, logical_date: str) -> str:
    resp = requests.post(
        f"{BASE}/api/v2/dags/{dag_id}/dagRuns",
        headers=auth_headers(),
        json={"logical_date": logical_date},
    )
    body = resp.json()
    run_id = body.get("dag_run_id")
    if not run_id:
        # 409 = a run already exists for this logical_date; other 4xx/5xx are failures too
        raise TriggerFailed(f"{resp.status_code}: {body}")
    return run_id

The beauty of this criterion is that it's status-code agnostic: whatever the server answers, a body without dag_run_id means the trigger did not happen — one check covers every failure shape.

Boundary cases: the rejection is sometimes exactly what you want​

Worth stating the other side: if your logical_date is the business date, the unique constraint is your idempotency guard. Backfilling the same day twice — the second trigger gets a 409 and no duplicate run is created. In that scenario the move is not "make the trigger succeed" but "clear and rerun the existing run". Don't mix the two:

Also: manual triggers without a logical_date get a manual__<timestamp> run_id and corresponding logical_date from Airflow — inherently collision-free. The ones who hit this are callers constructing their own logical_date values.

FAQ​

What happens if I trigger the same Airflow DAG run twice via the API?​

It gets rejected by a unique constraint: re-triggering with an existing logical_date returned HTTP 409 (Unique constraint violation) with no dag_run_id in the body, and the DAG never ran. Callers that only log the request miss the failure entirely.

Why was my Airflow dagRun triggered but nothing ran?​

The most common cause is a duplicate logical_date — Airflow enforces (dag_id, logical_date) uniqueness and answers 409, which an unchecked caller never notices. Rule: a trigger only succeeded if the response body contains a dag_run_id.

Can logical_date repeat in Airflow?​

Not within the same DAG — (dag_id, logical_date) carries a unique constraint and dag_run_id is a primary key. The rejection is by design and doubles as an idempotency guard for business-date-based triggers.