title: TemplateNotFound when using Airflow's PostgresOperator with Jinja templating and SQL
body: <p>When trying to use Airflow's templating capabilities (via Jinja2) with the PostgresOperator, I've been unable to get things to render. It's quite possible I'm doing something wrong, but I'm pretty lost as to what the issue might be. Here's an example to reproduce the TemplateNotFound error I've been getting:</p>
  
  <p><strong>airflow.cfg</strong></p>
  
  <pre><code>airflow_home = /home/gregreda/airflow
  dags_folder = /home/gregreda/airflow/dags
  </code></pre>
  
  <p><strong>relevant DAG and variables</strong></p>
  
  <pre><code>default_args = {
      'owner': 'gregreda',
      'start_date': datetime(2016, 6, 1),
      'schedule_interval': None,
      'depends_on_past': False,
      'retries': 3,
      'retry_delay': timedelta(minutes=5)
  }
  
  this_dag_path = '/home/gregreda/airflow/dags/example_csv_to_redshift'
  dag = DAG(
      dag_id='example_csv_to_redshift',
      schedule_interval=None,
      default_args=default_args
  )
  </code></pre>
  
  <p><strong>/example_csv_to_redshift/csv_to_redshift.py</strong></p>
  
  <pre><code>copy_s3_to_redshift = PostgresOperator(
      task_id='load_table',
      sql=this_dag_path + '/copy_to_redshift.sql',
      params=dict(
          AWS_ACCESS_KEY_ID=Variable.get('AWS_ACCESS_KEY_ID'),
          AWS_SECRET_ACCESS_KEY=Variable.get('AWS_SECRET_ACCESS_KEY')
      ),
      postgres_conn_id='postgres_redshift',
      autocommit=False,
      dag=dag
  )
  </code></pre>
  
  <p><strong>/example_csv_to_redshift/copy_to_redshift.sql</strong></p>
  
  <pre><code>COPY public.table_foobar FROM 's3://mybucket/test-data/import/foobar.csv'
  CREDENTIALS 'aws_access_key_id={{ AWS_ACCESS_KEY_ID }};aws_secret_access_key={{ AWS_SECRET_ACCESS_KEY }}'
  CSV
  NULL as 'null'
  IGNOREHEADER as 1;
  </code></pre>
  
  <p>Calling <code>airflow render example_csv_to_redshift load_table 2016-06-14</code> throws the exception below. Note I'm running into this issue for another DAG as well, which is why you see the path with <code>example_redshift_query_to_csv</code> mentioned.</p>
  
  <pre><code>[2016-06-14 21:24:57,484] {__init__.py:36} INFO - Using executor SequentialExecutor
  [2016-06-14 21:24:57,565] {driver.py:120} INFO - Generating grammar tables from /usr/lib/python2.7/lib2to3/Grammar.txt
  [2016-06-14 21:24:57,596] {driver.py:120} INFO - Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
  [2016-06-14 21:24:57,763] {models.py:154} INFO - Filling up the DagBag from /home/gregreda/airflow/dags
  [2016-06-14 21:24:57,828] {models.py:2040} ERROR - /home/gregreda/airflow/dags/example_redshift_query_to_csv/export_query_to_s3.sql
  Traceback (most recent call last):
    File "/usr/local/lib/python2.7/dist-packages/airflow/models.py", line 2038, in resolve_template_files
      setattr(self, attr, env.loader.get_source(env, content)[0])
    File "/usr/local/lib/python2.7/dist-packages/jinja2/loaders.py", line 187, in get_source
      raise TemplateNotFound(template)
  TemplateNotFound: /home/gregreda/airflow/dags/example_redshift_query_to_csv/export_query_to_s3.sql
  [2016-06-14 21:24:57,834] {models.py:2040} ERROR - /home/gregreda/airflow/dags/example_csv_to_redshift/copy_to_redshift.sql
  Traceback (most recent call last):
    File "/usr/local/lib/python2.7/dist-packages/airflow/models.py", line 2038, in resolve_template_files
      setattr(self, attr, env.loader.get_source(env, content)[0])
    File "/usr/local/lib/python2.7/dist-packages/jinja2/loaders.py", line 187, in get_source
      raise TemplateNotFound(template)
  TemplateNotFound: /home/gregreda/airflow/dags/example_csv_to_redshift/copy_to_redshift.sql
  Traceback (most recent call last):
    File "/usr/local/bin/airflow", line 15, in &lt;module&gt;
      args.func(args)
    File "/usr/local/lib/python2.7/dist-packages/airflow/bin/cli.py", line 359, in render
      ti.render_templates()
    File "/usr/local/lib/python2.7/dist-packages/airflow/models.py", line 1409, in render_templates
      rendered_content = rt(attr, content, jinja_context)
    File "/usr/local/lib/python2.7/dist-packages/airflow/models.py", line 2017, in render_template
      return jinja_env.get_template(content).render(**context)
    File "/usr/local/lib/python2.7/dist-packages/jinja2/environment.py", line 812, in get_template
      return self._load_template(name, self.make_globals(globals))
    File "/usr/local/lib/python2.7/dist-packages/jinja2/environment.py", line 774, in _load_template
      cache_key = self.loader.get_source(self, name)[1]
    File "/usr/local/lib/python2.7/dist-packages/jinja2/loaders.py", line 187, in get_source
      raise TemplateNotFound(template)
  jinja2.exceptions.TemplateNotFound: /home/gregreda/airflow/dags/example_csv_to_redshift/copy_to_redshift.sql
  </code></pre>
  
  <p>Any ideas towards a fix are much appreciated.</p>