@Override
  public float getProgress() {
    //not implemented currently.
    return 0;
  }
Callback invoked from Yarn when containers are allocated. This translates the yarn callbacks into Samza
specific ones.
@param containers the list of {@link Container} returned by Yarn.
samza-yarn3/src/main/java/org/apache/samza/job/yarn/YarnClusterResourceManager.java