title: Datapipeline task stuck in WAITING_FOR_RUNNER state
body: <p>I have created a simple ShellCommandActivity which echos some text. It runs on a plain ec2 (vpc) instance. I see that the host has spinned up but it never executes the tasks and the task remains in <code>WAITING_FOR_RUNNER</code> status. After all the retries I get this error </p>
  
  <pre><code>Resource is stalled. Associated tasks not able to make progress. 
  </code></pre>
  
  <p>I followed this <a href="http://docs.aws.amazon.com/datapipeline/latest/DeveloperGuide/dp-check-when-run-fails.html#dp-waiting-for-runner" rel="nofollow noreferrer">troubleshoot-link</a> but it didn't resolve my problem. </p>
  
  <p>Here is the json description of the pipeline:</p>
  
  <pre><code>{
    "objects": [
      {
        "resourceRole": "DataPipelineDefaultResourceRole",
        "role": "DataPipelineDefaultRole",
        "name": "ec2-compute",
        "id": "ResourceId_viWO9",
        "type": "Ec2Resource"
      },
      {
        "failureAndRerunMode": "CASCADE",
        "resourceRole": "DataPipelineDefaultResourceRole",
        "role": "DataPipelineDefaultRole",
        "pipelineLogUri": "s3://xyz-logs/",
        "scheduleType": "ONDEMAND",
        "name": "Default",
        "id": "Default"
      },
      {
        "name": "EchoActivity",
        "id": "ShellCommandActivityId_kc8xz",
        "runsOn": {
          "ref": "ResourceId_viWO9"
        },
        "type": "ShellCommandActivity",
        "command": "echo HelloWorld"
      }
    ],
    "parameters": []
  }
  </code></pre>
  
  <p>What could be the problem here?</p>
  
  <p>Thanks in advance.</p>