DAG should look like

• start_dag >> check_file_exists >> end_dag
• in case any task fails, the dag should fail (later we will integrate with free slack app so you get a notification on slack)
• for file you can use example we draw on paper

• add your full project id
• add your email used in google cloud
• add your service account email (do NOT add json key)

so in case you won't be able to proceed with your credit card I can give you access to mine google account (we will put very small sample data so we stay within Free Tier)