Airflow: Fix for DAG not found in serialized_dag table

README

While rapidly starting and stoping and changing dags during development, you may run into errors look like this for one or more of the dags:

dag_talk_examples-airflow-scheduler-1  | [2023-07-11 21:07:54,767] {scheduler_job.py:1063} ERROR - DAG 'zimmerman-garcia-and-henry-incremental' not found in serialized_dag table
dag_talk_examples-airflow-scheduler-1  | [2023-07-11 21:07:55,800] {scheduler_job.py:1063} ERROR - DAG 'zimmerman-garcia-and-henry-full' not found in serialized_dag table
dag_talk_examples-airflow-scheduler-1  | [2023-07-11 21:07:55,802] {scheduler_job.py:1063} ERROR - DAG 'zimmerman-garcia-and-henry-incremental' not found in serialized_dag table
dag_talk_examples-airflow-scheduler-1  | [2023-07-11 21:07:56,577] {scheduler_job.py:1063} ERROR - DAG 'zimmerman-garcia-and-henry-incremental' not found in serialized_dag table
dag_talk_examples-airflow-scheduler-1  | [2023-07-11 21:07:56,579] {scheduler_job.py:1063} ERROR - DAG 'zimmerman-garcia-and-henry-full' not found in serialized_dag table

This will fix it.

Pulled from this discussion: https://github.com/apache/airflow/issues/18843

repair_missing_dags.py

# at some point while starting and stopping the cluster, the dags were not serialized properly.
#
# symptoms:
#   - the dags are not visible in the UI
#   - the dags are not running
#   - the dags are not in the airflow db
#   - the dags are in the dags folder
#   - "ERROR - DAG '{dag name}' not found in serialized_dag table" error log entries 
#   
# This script will fix that.
#

from airflow.models import DagBag
from airflow.models.serialized_dag import SerializedDagModel

dag_bag = DagBag()

# Re-serialize any DAGs missing from the database.
for dag_id in dag_bag.dag_ids:
    if not SerializedDagModel.get(dag_id):
        dag = dag_bag.get_dag(dag_id)
        SerializedDagModel.write_dag(dag)