title: How to combine multiple DAGs in Airflow
body: <p>I really need to know how to use Airflow to have multiple DAGs call each other (e.g. <code>DAG_1 &gt;&gt; DAG_2</code>) similar to how it uses the upstream/downstream operators to run tasks within a DAG.  I need to know how to set this up so Airflow will run <code>DAG_1</code>, then will run <code>DAG_2</code> once <code>DAG_1</code> has completed successfully.</p>
  
  <p>Preferably I would like to have <code>DAG_1</code> and <code>DAG_2</code> in separate files within the Airflow <strong>dag</strong> folder, then either have <code>DAG_2</code> call <code>DAG_1</code> as a pre-step at the start of its run, or have a separate "main" DAG which creates and runs a DAG where each task is another DAG rather than a task operator.</p>
  
  <p>If anyone knows how to do this, please let me know, I really need some help here.  I will also accept making and connecting two separate DAGs in the same file if anyone knows how to do that, but preferably the linked DAGs will be in different files.</p>
  
  <p>Thank you in advance for your assistance.</p>