It's not wasting system resources if the "legacy" VM offers many more useful features than a container. There is nothing legacy about a virtual machine, it simply serves a different purpose and is useful to a different set of people. I have nothing against Docker, but this text reads like propaganda rather than useful information. I especially love the way they inserted a host OS into a virtualisation stack to make it look less efficient - the host OS doesn't sit there in a proper hypervisor setup. I'm not saying docker isn't lighter, but they shouldn't need to bodge a diagram to say that.