title: how does luigi handles task failure?
body: <p>I am beginning to use Luigi.
  I have build a pipeline that does several tasks, and I have been careful enough to make sure the tasks work well. So the pipeline works well.
  While building the pipeline, in the times that tasks had failures, they got reported with <code>:(</code> and I edited them till they work fine.</p>
  <p>So let's say I have a pipeline that does</p>
  <pre><code>Task1--&gt;Task2--&gt; Task3
  </code></pre>
  <p>In that case, if Task2 fails, Task3 is not executed and the pipeline stops at that. Usually because there was an error writing the Task2.</p>
  <p>Now imagine that there are 5 &quot;Task1&quot;s  , 5 &quot;Task2&quot;s and one &quot;Task3&quot;. So Task3 is kind of a summary task.</p>
  <p>I would like my pipeline <em>not to stop</em> whenever there is a failure but skip (and perhaps log the failure) and continue with the next case. (These &quot;failures&quot; will not be because the task is badly written but because let's say the data that is input to these task is corrupted in a real case scenario)</p>
  <p>Something like</p>
  <p><a href="https://i.stack.imgur.com/bCZRG.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bCZRG.png" alt="Pipeline with failures" /></a></p>
  <p>There you can see that Task1 is executed before Task2.
  The Tasks marked in red are &quot;failures&quot;.</p>
  <p>So what I would like the pipeline to do is to execute Tasks 1 and Tasks 2, log if there are failures and continue and finally summarize with Task3 (even including some kind of report that there were failures)</p>
  <p>How can I do this with Luigi?</p>