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CHAPTER 1 What Are Containers? 7 These materials are © 2017 John Wiley & Sons, Inc. Any dissemination, distribution, or unauthorized use is strictly prohibited. Compare Figure 1-2 to Figure 1-1, and you'll notice some key dif- ferences. First, the container engine abstraction layer is attached. Second, even on bare metal, with the container engine, you can run multiple isolated workloads on the same hardware. Previ- ously, this ability was the purview of a virtualization solution, which, again, also required a compete OS per instance. Now, you can do this without a full hypervisor in place and without all the overhead of a bunch of operating systems. And even when you do run a hypervisor, you still get a lot of bene- fits. Virtualization has been popular for a lot more than just work- load density and saving hardware money. By turning servers into software, you've gained the ability to manipulate those workloads in powerful ways. This has led to a rise in application availability capabilities, new disaster recovery opportunities, and new ways to programmatically manage workloads. To maintain these benefits, you can run container engines on top of your existing virtualization stack, which is shown in the bot- tom part of Figure 1-2. As is the case with bare metal, you can deploy multiple container engines — and thus, multiple isolated workloads — on top of a single virtual machine. This way, you get those sweet virtualization benefits while, at the same time, even further increasing workload density thanks to containers. The key takeaway from this section is this: You can run containers wherever you like, whether that's on bare metal, in a virtualized environment, or in the cloud. When run in your local data cen- ter, containers provide workload density capabilities that can't be matched by virtualization alone. In fact, when HPE tested consol- idation of a single host with eight MySQL VM workloads to eight FIGURE 1-2: Improved density with the addition of containers.