What they have done is turn on the partial aggregation via the setting: yarn.nodemanager.log-aggregation.roll-monitoring-interval-seconds.
That will allow you to grab some of the logs using the command line.
We do not support this in CDH although we have the exact same code in CDH is available upstream. We have tested the setting and found that it breaks log access via the different UIs in multiple ways. So you get a working command line in 99% of the cases but when you try to use the RM or AM UIs it breaks almost always. The way it breaks changes over time for the same application. That is not a feature that we can support in the state it is at the moment.