System & Network Administration Virtualization PDF

System & Network Administration Virtualization Le Hai Duong, PhD. ([email protected])  Overview ❏ Run multiple operating system instances (“guest”) concurrently on the same physical hardware ❏ From the user’s point of view, a virtual server behaves like a full-fledged physica...

System & Network Administration Virtualization Le Hai Duong, PhD. ([email protected])  Overview ❏ Run multiple operating system instances (“guest”) concurrently on the same physical hardware ❏ From the user’s point of view, a virtual server behaves like a full-fledged physical server ❏ Led to the rise of on-demand, Internet-connected virtual servers: the infrastructure we now know as cloud computing ❏ A new era of OS abstraction arises in the form of containers  Virtualization vs Containerization ❏ virtualization (server virtualization)→ guest operating systems run within the context of virtualized hardware ❏ OS-level virtualization → containerization  Hypervisor ❏ Hypervisor (virtual machine monitor) → software layer that mediates between virtual machines (VMs) and the underlying hardware ❏ e.g., ❏ VMware ESX, XenServer, FreeBSD bhyve ❏ the Linux kernel-based virtual machine (KVM) converts the Linux kernel into a hypervisor  Hypervisor (conti.) ❏ Full virtualization → fully emulate the underlying hardware, defining virtual replacements for all the basic computing resources: hard disks, network devices, interrupts, motherboard hardware, BIOSs, and so on ❏ runs guests without modification ❏ incurs a performance penalty because the hypervisor must constantly translate between the system’s actual hardware and the virtual hardware exposed to guests ❏ separate the task of maintaining multiple environments (virtualization) from the task of simulating the hardware within each environment (emulation) ❏ e.g., The most common emulation package used in these systems is an open source project called QEMU  Hypervisor (conti.) ❏ Paravirtualization → modified guest operating systems detect their virtualized state and actively cooperate with the hypervisor to access hardware ❏ improves performance by an order of magnitude or more ❏ guest operating systems need substantial updates to run this way ❏ e.g., Xen hypervisor  Hypervisor (conti.) ❏ Hardware-assisted virtualization (a.k.a accelerated virtualization) → CPU features ( Intel VT and AMD-V) facilitate virtualization ❏ CPU and memory controller are virtualized by the hardware ❏ Performance is very good ❏ Guest operating systems need not know that they’re running on a virtualized CPU  Type 1 vs. type 2 hypervisors bare-metal or native hypervisor → User-space applications that run on top runs directly on the hardware without a of another general-purpose OS (e.g., supporting OS (e.g., XenServer, VMware Workstation, VirtualBox) VMware ESXi)  Live Migration ❏ Virtual machines can move between hypervisors running on different physical hardware in real time without interruptions in service or loss of connectivity ❏ memory dance → hypervisor copies changes from the source to the destination, and as soon as the memory is identical between the two, the migration completes ❏ helpful for high-availability, load balancing, disaster recovery, server maintenance, and general system flexibility  Virtual machine images ❏ Templates of configured operating systems that a hypervisor can load and execute ❏ Can take a snapshot of a virtual machine to create an image ❏ Images are portable among systems even if their actual hardware differs ❏ There are conversion tools that port images among hypervisors Containerization ❏ OS-level virtualization does not use a hypervisor ❏ Rely on kernel features that isolate processes from the rest of the system ❏ Each process “container” or “jail” has a private root filesystem and process namespace ❏ Contained processes share the kernel and other services of the host OS, but cannot access files or resources outside of their containers ❏ Resource overhead of OS-level virtualization is low, offer near-native performance ❏ Precludes the use of multiple operating systems ❏ E.g., Linux’s LXC, Docker containers, and FreeBSD jails ❏ The containers-on-VMs architecture is standard for containerized applications that need to run on public cloud instances  Packer ❏ A tool for building virtual machine images from a specification file ❏ Can build images for a variety of virtualization and cloud platforms ❏ Instead of manually applying changes to images, you modify a template that describes the image in abstract terms ❏ Packer configurations are JSON files  Vagrant ❏ A wrapper that sits on top of virtualization platforms such as VMware, VirtualBox, and Docker ❏ It is not itself a virtualization platform ❏ Simplify virtual environment provisioning and configuration ❏ Its mission is to quickly and easily create disposable, preconfigured development environments that closely mirror production environments