In Chapter 1, Exploring the Azure Cloud, we had a short introduction to containers. So, let's go ahead and cover containers in more detail. We know that VMs are run on a hypervisor, and for each purpose, in most cases you have to create a separate VM to isolate the environments. VMs will have a guest OS, such as Linux, and on top of that we will install the software we require. There will be scenarios where you have to deploy a large number of VMs for testing. If you are using an on-premises infrastructure running Hyper-V, you have to think about resource utilization—that is, how much memory, CPU, and so on you will use for each VM. If you are deploying in Azure, you have to think about the cost as well. You might need some VMs only for a couple of hours just to test something, but the footprints of these VMs are large; they're complete computers that are running virtually. Another problem is compatibility issues. Let's assume...