The genesis of this article was a financial industry luncheon in New York City a couple of years back at which I was invited to speak. The topic was this new "containers" thing: what it was, where it was going, and how it could best be used. Of particular interest was how containers related to virtual machines (VMs).
At this point, it's worth remembering the context in which server virtualization and its VMs became such a popular technology, fundamentally changing how many datacenters were operated and spawning a mini-industry of complementary vendors and products. Although initially introduced as primarily a tool for developers, virtualization rapidly became instead a way to carve out multiple virtual servers from a single physical server. This server consolidation was initially driven by cost-cutting, a popular pasttime after the dot-com bubble popped.