Do not silently allow the use of undefined variables in jinja2 templates #11016
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Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contribution Guide (https://github.com/apache/airflow/blob/master/CONTRIBUTING.rst)
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origamislayer
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@lattwood Can you add etry in UPDATING.md? This will allow us to avoid surprises after migrating to Airflow 2.0 |
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@mik-laj will do |
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@mik-laj done |
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This can have *extremely* bad consequences. After this change, a jinja2
template like the one below will cause the task instance to fail, if the
DAG being executed is not a sub-DAG. This may also display an error on
the Rendered tab of the Task Instance page.
task_instance.xcom_pull('z', key='return_value', dag_id=dag.parent_dag.dag_id)
Prior to the change in this commit, the above template would pull the
latest value for task_id 'z', for the given execution_date, from *any DAG*.
If your task_ids between DAGs are all unique, or if DAGs using the same
task_id always have different execution_date values, this will appear to
act like dag_id=None.
Our current theory is SQLAlchemy/Python doesn't behave as expected when
comparing `jinja2.Undefined` to `None`.
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@mik-laj, docs added, PR is green! |
kaxil
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Sep 24, 2020
potiuk
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Sep 25, 2020
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Awesome work, congrats on your first merged pull request! |
ashb
reviewed
Sep 28, 2020
| ```python | ||
| import jinja2 | ||
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| dag = DAG('simple_dag', template_undefined=jinja2.Undefined) |
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Is it also possible on a template-by-template basis to do it as {{ something | default "x" }}?
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Yes, I believe all standard jinja2 templating features are still available.
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This can have extremely bad consequences. After this change, a jinja2 template like the one below will cause the task instance to fail, if the DAG being executed is not a sub-DAG. This may also display an error on the Rendered tab of the Task Instance page.
task_instance.xcom_pull('z', key='return_value', dag_id=dag.parent_dag.dag_id)Prior to the change in this commit, the above template would pull the latest value for task_id 'z', for the given execution_date, from any DAG. If your task_ids between DAGs are all unique, or if DAGs using the same task_id always have different execution_date values, this will appear to act like dag_id=None.
Our current theory is SQLAlchemy/Python doesn't behave as expected when comparing
jinja2.UndefinedtoNone.Admittedly this issue boils down to PEBKAC, but this is also a case of Airflow not doing the (perceived) right thing in the face of ambiguity, and this PR fixes that up.
I did find this note about why it was only set to
jinja2.Undefined, but given the way this can fail (and the difficulty in tracking down the root cause), I strongly feel this warrants breaking backwards compatibility with DAGs/task instances that are attempting to erroneously use undefined variables.#4951 (comment)