Virtualization is the secret sauce behind cloud computing, as it allows a single piece of hardware to be shared by multiple customers. Concepts like multitenancy and resource pooling would not exist as they do today — and you wouldn’t be reading this book — if it weren’t for the advent of virtualization!
Virtualization offers many clear benefits. Following is a list of some of the most noteworthy:
- Increases scalability: Virtualized environments are designed to grow as your demand grows. Instead of buying new hardware, you simply spin up additional virtual instances.
- Allows faster resource provisioning: It’s much quicker and easier to spin up virtualized hardware from a console than it is to physically boot-up multiple pieces of hardware.
- Reduces downtime: Restoring or redeploying physical hardware takes a lot of time, especially at scale. Failover for virtualized resources can happen much more quickly, which means your systems remain up and running longer.
- Avoids vendor lock-in: Virtualization abstracts software from hardware, meaning your virtualized resources are more portable than their physical counterparts. Unhappy with your vendor? Pack up your VMs and move to another one!
- Saves time (and money): Virtualized resources can be easily centrally managed, reducing the need for personnel and equipment to maintain your infrastructure. In addition, less hardware usually means less money.
The most common implementation of virtualization is the hypervisor. A hypervisor is a computing layer that allows multiple guest Operating Systems to run on a single physical host device. The following figure shows an overview of hypervisor architecture.
Hypervisor overview.The hypervisor abstracts software from hardware and allows each of the guest OSes to share the host’s hardware resources, while giving the guests the impression that they’re all alone on that host. The two categories of hypervisors are Type 1 and Type 2. A Type 1 hypervisor is also known as a bare metal hypervisor, as it runs directly on the hardware. Type 2 hypervisors, however, run on the host’s Operating System. This figure shows a comparison of the two.
Type 1 versus Type 2 hypervisors.Despite all the advantages of virtualization, and hypervisors specifically, you, as a CCSP candidate, should remember some challenges:
- Hypervisor security: The hypervisor is an additional piece of software, hardware, or firmware that sits between the host and each guest. As a result, it expands the attack surface and comes with its own set of vulnerabilities that the good guys must discover and patch before the bad guys get to them. If not fixed, hypervisor flaws can lead to external attacks on VMs or even VM-to-VM attacks, where one cloud tenant can access or compromise another tenant’s data.
- VM security: Virtual machines are nothing more than files that sit on a disk or other storage mechanism. Imagine your entire home computer wrapped up into a single icon that sits on your desktop — that’s pretty much what a virtual machine comes down to. If not sufficiently protected, a VM image is susceptible to compromise while dormant or offline. Use controls like Access Control Lists (ACLs), encryption, and hashing to protect the confidentiality and integrity of your VM files.
- Network security: Network traffic within virtualized environments cannot be monitored and protected by physical security controls, such as network-based intrusion detection systems. You must select appropriate tools to monitor inter- and intra-VM network traffic.
The concept of virtual machine introspection (VMI) allows a hypervisor to monitor its guest Operating Systems during runtime. Not all hypervisors are capable of VMI, but it’s a technique that can prove invaluable for securing VMs during operation.
- Resource utilization: If not properly configured, a single VM can exhaust a host’s resources, leaving other VMs out of luck. Resource utilization is where the concept of limits (discussed in the “Reservations, limits, and shares” section of this chapter) comes in handy. It’s essential that you manage VMs as if they share a pool of resources — because they do!