Airflow - how to make EmailOperator html_content dynamic? - airflow

Question

I'm looking for a method that will allow the content of the emails sent by a given EmailOperator task to be set dynamically. Ideally I would like to make the email contents dependent on the results of an xcom call, preferably through the html_content argument.
alert = EmailOperator(
task_id=alertTaskID,
to='please#dontreply.com',
subject='Airflow processing report',
html_content='raw content #2',
dag=dag
)
I notice that the Airflow docs say that xcom calls can be embedded in templates. Perhaps there is a way to formulate an xcom pull using a template on a specified task ID then pass the result in as html_content? Thanks

Answer 1

Use PythonOperator + send_email instead:
from airflow.operators import PythonOperator
from airflow.utils.email import send_email
def email_callback(**kwargs):
with open('/path/to.html') as f:
content = f.read()
send_email(
to=[
# emails
],
subject='subject',
html_content=content,
)
email_task = PythonOperator(
task_id='task_id',
python_callable=email_callback,
provide_context=True,
dag=dag,
)

Answer 2

For those looking for an exact example of using jinja template with EmailOperator, here is one
from airflow.operators.email_operator import EmailOperator
from datetime import timedelta, datetime
email_task = EmailOperator(
to='some#email.com',
task_id='email_task',
subject='Templated Subject: start_date {{ ds }}',
params={'content1': 'random'},
html_content="Templated Content: content1 - {{ params.content1 }} task_key - {{ task_instance_key_str }} test_mode - {{ test_mode }} task_owner - {{ task.owner}} hostname - {{ ti.hostname }}",
dag=dag)
You can test run the above code snippet using
airflow test dag_name email_task 2017-05-10

Answer 3

might as well answer this myself. Turns out it's fairly straight forward using the template+xcom route. This code snippet works in the context of an already defined dag. It uses the BashOperator instead of EmailOperator because it's easier to test.
def pushparam(param, ds, **kwargs):
kwargs['ti'].xcom_push(key='specificKey', value=param)
return
loadxcom = PythonOperator(
task_id='loadxcom',
python_callable=pushparam,
provide_context=True,
op_args=['your_message_here'],
dag=dag)
template2 = """
echo "{{ params.my_param }}"
echo "{{ task_instance.xcom_pull(task_ids='loadxcom', key='specificKey') }}"
"""
t5 = BashOperator(
task_id='tt2',
bash_command=template2,
params={'my_param': 'PARAMETER1'},
dag=dag)
can be tested on commandline using something like this:
airflow test dag_name loadxcom 2015-12-31
airflow test dag_name tt2 2015-12-31
I will eventually test with EmailOperator and add something here if it doesn't work...