title: Airflow DAGs tasks not running when i run DAG despite tasks working fine when i test them
body: <p>I have the following DAG defined in code:</p>
  <pre><code>from datetime import timedelta, datetime
  import airflow
  from airflow import DAG
  from airflow.operators.docker_operator import DockerOperator
  from airflow.contrib.operators.ecs_operator import ECSOperator
  
  default_args = {
      'owner': 'airflow',
      'retries': 1,
      'retry_delay': timedelta(minutes=5),
      'start_date': datetime(2018, 9, 24, 10, 00, 00)
  }
  
  dag = DAG(
      'data-push',
      default_args=default_args,
      schedule_interval='0 0 * * 1,4',
  )    
  
  
  colors = ['blue', 'red', 'yellow']
  for color in colors:
      ECSOperator(dag=dag,
              task_id='data-push-for-%s' % (color),
              task_definition= 'generic-push-colors',
              cluster= 'MY_ECS_CLUSTER_ARN',
              launch_type= 'FARGATE',
              overrides={
                  'containerOverrides': [
                      {
                          'name': 'push-colors-container',
                          'command': [color]
                      }
                  ]
              },
              region_name='us-east-1',
              network_configuration={
                      'awsvpcConfiguration': {
                             'securityGroups': ['MY_SG'],
                             'subnets': ['MY_SUBNET'],
                             'assignPublicIp': &quot;ENABLED&quot;
                         }
                 }, 
      )
  </code></pre>
  <p>This should create a DAG with 3 tasks, one for each color in my colors list.</p>
  <p>This seems good, when i run:</p>
  <pre><code>airflow list_dags
  </code></pre>
  <p>I see my dag listed:</p>
  <pre><code>data-push
  </code></pre>
  <p>And when I run:</p>
  <pre><code>airflow list_tasks data-push
  </code></pre>
  <p>I see my three tasks appear as they should:</p>
  <pre><code>data-push-for-blue
  data-push-for-red
  data-push-for-yellow
  </code></pre>
  <p>I then test run one of my tasks by entering the following into terminal:</p>
  <pre><code>airflow run data-push data-push-for-blue 2017-1-23
  </code></pre>
  <p>And this runs the task, which I can see appear in my ECS cluster on the aws dashboard so I know for a fact the task runs on my ECS cluster and the data is pushed succesfully and everything is great.</p>
  <p>Now when I try and run the DAG data-push from the Airflow UI is where i run into a problem.</p>
  <p>I run:</p>
  <pre><code>airflow initdb
  </code></pre>
  <p>followed by:</p>
  <pre><code>airflow webserver
  </code></pre>
  <p>and now go into the airflow UI at localhost:8080.</p>
  <p>I see the dag data-push in the list of dags, click it, and then to test run the entire dag i click the &quot;Trigger DAG&quot; button. I don't add any configuration json and then click 'Trigger'. The tree view for the DAG then shows a green circle on the right of the tree structure, seemingly indicating the DAG is 'running'. But the green circle just stays there for ages and when I manually check my ECS dashboard I see no tasks actually running so nothing is happening after triggering the DAG from the Airflow UI, despite the tasks working when i manually run them from the CLI.</p>
  <p>I am using the SequentialExecutor if that matters.</p>
  <p>My two main theories as to why the triggering the DAG does nothing when running the individual tasks from the CLI works are that maybe I am missing something in my python code where I define the dag (maybe because I dont specifiy any dependencies for the tasks?) or that I am not running the airflow scheduler but if I am manually triggering the DAGS from the Airflow UI i don't see why the scheduler would need to be running and why it wouldn't show me an error saying this is a problem.</p>
  <p>Any ideas?</p>