Airflow Xcom not getting resolved return task_instance string - airflow

Question

I am facing an odd issue with xcom_pull where it is always returning back a xcom_pull string
"{{ task_instance.xcom_pull(dag_id = 'cf_test',task_ids='get_config_val',key='http_con_id') }}"
My requirement is simple I have pushed an xcom using python operator and with xcom_pull I am trying to retrieve the value and pass it as an http_conn_id for SimpleHttpOperator but the variable is returning a string instead of resolving xcom_pull value.
Python Operator is successfully able to push XCom.
Code:
from datetime import datetime
import simplejson as json
from airflow.models import DAG
from airflow.operators.dummy_operator import DummyOperator
from airflow.operators.python_operator import PythonOperator
from airflow.providers.http.operators.http import SimpleHttpOperator
from google.auth.transport.requests import Request
default_airflow_args = {
"owner": "divyaansh",
"depends_on_past": False,
"start_date": datetime(2022, 5, 18),
"retries": 0,
"schedule_interval": "#hourly",
}
project_configs = {
"project_id": "test",
"conn_id": "google_cloud_storage_default",
"bucket_name": "test-transfer",
"folder_name": "processed-test-rdf",
}
def get_config_vals(**kwargs) -> dict:
"""
Get config vals from airlfow variable and store it as xcoms
"""
task_instance = kwargs["task_instance"]
task_instance.xcom_push(key="http_con_id", value="gcp_cloud_function")
def generate_api_token(cf_name: str):
"""
generate token for api request
"""
import google.oauth2.id_token
request = Request()
target_audience = f"https://us-central1-test-a2h.cloudfunctions.net/{cf_name}"
return google.oauth2.id_token.fetch_id_token(
request=request, audience=target_audience
)
with DAG(
dag_id="cf_test",
default_args=default_airflow_args,
catchup=False,
render_template_as_native_obj=True,
) as dag:
start = DummyOperator(task_id="start")
config_vals = PythonOperator(
task_id="get_config_val", python_callable=get_config_vals, provide_context=True
)
ip_data = json.dumps(
{
"bucket_name": project_configs["bucket_name"],
"file_name": "dummy",
"target_location": "/valid",
}
)
conn_id = "{{ task_instance.xcom_pull(dag_id = 'cf_test',task_ids='get_config_val',key='http_con_id') }}"
api_token = generate_api_token("new-cp")
cf_task = SimpleHttpOperator(
task_id="file_decrypt_and_validate_cf",
http_conn_id=conn_id,
method="POST",
endpoint="new-cp",
data=json.dumps(
json.dumps(
{
"bucket_name": "test-transfer",
"file_name": [
"processed-test-rdf/dummy_20220501.txt",
"processed-test-rdf/dummy_20220502.txt",
],
"target_location": "/valid",
}
)
),
headers={
"Authorization": f"bearer {api_token}",
"Content-Type": "application/json",
},
do_xcom_push=True,
log_response=True,
)
print("task new-cp", cf_task)
check_flow = DummyOperator(task_id="check_flow")
end = DummyOperator(task_id="end")
start >> config_vals >> cf_task >> check_flow >> end
Error Message:
raise AirflowNotFoundException(f"The conn_id `{conn_id}` isn't defined") airflow.exceptions.AirflowNotFoundException: The conn_id `"{{ task_instance.xcom_pull(dag_id = 'cf_test',task_ids='get_config_val',key='http_con_id') }}"` isn't defined
I have tried several different days but nothing seems to be working.
Can someone point me to the right direction here.
Airflow-version : 2.2.3
Composer-version : 2.0.11

Answer 1

In SimpleHttpOperator the http_conn_id parameter is not templated field thus you can not use Jinja engine with it. This means that this parameter can not be rendered. So when you pass "{{ task_instance.xcom_pull(dag_id = 'cf_test',task_ids='get_config_val',key='http_con_id') }}" to the operator you expect it to be replaced during runtime with the value stored in Xcom by previous task but in fact Airflow consider it just as a regular string this is also what the exception tells you. It actually try to search a connection with the name of your very long string but couldn't find it so it tells you that the connection is not defined.
To solve it you can create a custom operator:
class MySimpleHttpOperator(SimpleHttpOperator):
template_fields = SimpleHttpOperator.template_fields + ("http_conn_id",)
Then you should replace SimpleHttpOperator with MySimpleHttpOperator in your DAG.
This change makes the string that you set in http_conn_id to be passed via the Jinja engine. So in your case the string will be replaced with the Xcom value as you expect.