Ha yes, it cannot reduce memory usage magically 
and the OS doesn’t have build and scripting tools whatsoever. The promised 40% is about the default not loaded OS footprint.
I had to increase the coreos KVM instance’s memory allocation from 1G, because of OOM errors in Discourse. However, it’s a good idea to run multiple dockers on the same image, for better memory utilization.
The other question is how we can leverage CoreOS’ cluster feature. The documentation usually refers to a kill - rm - pull - run sequence, while discourse_docker keeps the original container if available. Is there a technology which updates the docker image other than launcher rebuild?