public boolean isAlive() {
    return alive;
  }
Used to represent the heartbeat response between
the JobCoordinator and the containers.
{@link ContainerHeartbeatResponse#isAlive()} is set to <code>true</code>
iff. the heartbeat is valid.
samza-core/src/main/java/org/apache/samza/container/ContainerHeartbeatResponse.java