VL 3

Question 1

What is virtualization?

Answer 1

Computer architecture technology by which multiple virtual machines are multiplexed in the same hardware (access same hardware)
Creating resources in a layer abstracted from real hardware

Question 2

Objectives of virtualization

Answer 2

Resource sharing by many users at a time
Replace and upgrade hardware in the fly
Add new devices without reboot
Reduce down time
Offer administrative tasks (installing software) at runtime
Faster provisioning of multiple machines

Question 3

Modes of operation

Answer 3

Kernel mode: OS allows all CPU instructions to execute on the underlying hardware
Kernel codes do not execute in the USER mode
User mode: OS allows only a few instructions to be executed
If user apps have to execute privileged instructions, applications ask kernels to do the work

Question 4

System calls and CPUs

Answer 4

OS does:
Process Management, Memory Management, File Management, Network Management, Scheduling, Timing

Question 5

How many cycles does system call make?

Answer 5

Around 242

Question 6

Hypervisor: Bare Metal Virtualization

Answer 6

Guest Applications Ring 3
Guest OSs Ring 1
—————
VMM Ring 0
Hardware

Question 7

Hypervisor: Hosted Virtualization

Answer 7

Hypervisor (VMM) is loaded on top of OS.
Guest OS runs on hosted Hypervisors.
Parallels, oracle Virtualbox

Guest OS
VMM
—————
Host OS(Linux, MacOS)
Hardware

Question 8

Implementation: Full virtualization

Answer 8

Guest OS is not modified

Guest OS Ring 1
———————
VMM Ring 0
Hardware

Question 9

What happens if privileged instructions are executed in Full Virtualization?

Answer 9

They are trapped due to execution in less privileged ring.
VMM intercepts such traps and emulates instruction on the fly

Question 10

Impact of system calls

Answer 10

A binary translated system call with 32-but guest OS running on ring 1 takes around 2300 cycles
Reason: CPU issues fault message for every system call. Later, they were translated and executed

Question 11

Impact of I/O Virtualization

Answer 11

Bigger issue compared to CPU virtualization.
CPU could be added by replacing dual core CPU to quad cores
But memory bandwidth or data path or I/O chipset could not be easily modified/upgraded in a computing machine.
All guest OS should wait for physical I/O

Question 12

Impact of memory virtualization

Answer 12

Was introduced to reduce system crash
Memory management technique: maps programs memory addresses to the underlying physical machine memory
Adv: increased security; isolation; freeing applications

Question 13

Mapping in memory virtualization in VM

Answer 13

Programs memory Adresses are mapped to Virtual physical memory and then to physical memory => 2-stage mapping process for any guest OS

Question 14

GuestOS machine memory access, memory virtualization

Answer 14

Cannot directly access, VMM does mapping of addresses
The page table in VMM is called shadow page table

Question 15

Implementation: Para Virtualization

Answer 15

Guest OS needs to be modified at the source code level
Why not normal OS from Internet? Privileged instructions go directly to Hypervisor, because OS instructions are already translated in OS
Hypervisor provides interfaces to accommodate critical kernel operations like memory management

Question 16

Why is performance good in Para Virtualization?

Answer 16

Because it avoids unnecessary trapping of critical instructions

Question 17

Purpose of Hardware-assisted virtualization

Answer 17

Quickly identify the privilege instructions and efficiently execute them
=> one more high priority level VMX Root mode for VMM
Guest OS: ring 0

Question 18

Bare metal Virtualization: pros and cons

Answer 18

Barr metal can be slower
Resources requirements are comparatively low
High scalability
Multiple VMs can share a single machine/cluster
In cloud, 1000s of VMs are required
=> hosted virtualization is better solution in terms of scalability

Question 19

Hosted virtualization- OS level. How can be built ?

Answer 19

VMM is not b top ofHost OS
Built with namespaces and cgroups

Question 20

Linux Namespaces

Answer 20

Used to limit the views
Wrap a group of resources

Question 21

Kinds of namespaces

Answer 21

PID namespace: create another set of PID from PID 1 for that specific namespace
Cgroup namespace: offers new views to root directories for processes, isolates and manages resources
Network namespace: offers new view for network resources

Question 22

Cgroups - control groups

Answer 22

Limits application to a specific set of resources
Provides mechanism for aggregating/partitioning set of tasks

Question 23

Types of cgroups

Answer 23

Memory
CPU
Devices

Question 24

Memory cgroup

Answer 24

Memory resource controller
Creates a cgroup with a limited amount of memory
Features:
Accounting: how much memory pages are utilized by a specific group of running processes ?
Limiting: soft limit: memory allotted if available
Hard limit: memory is not allotted to group if tasks

Question 25

Impact exceeding hard limit of memory cgroup

Answer 25

Kernel triggers Out of memory killer process to kill any running processes Customize solution for handling hard limit

Question 26

Custom OOM Killer process

Answer 26

1. All processes are stopped processing 2. Notify user space 3. User could kill specific processes 4. Or, user could increase hard limit specified in cgroups 5. When done, unfreeze the group

Question 27

Containers

Answer 27

Uses kernel features (cgroups and namespaces) Provides environment where hardware is shared among multiple users Lightweight VM Less space Can get a shell on it via SSH Container 1 Container 2 Shared kernel of OS OS Machine

Question 28

Docker

Answer 28

Utilizes container technology Easily ports containers Replicates containers across environments

Question 29

Docker vs Virtual Machine

Answer 29

Problems with VM: size, memory, integration Repetition of Guest OS is avoided in docker through union file system

Question 30

Docker Containers: Operations

Answer 30

Caches the layers for the first time of building them => fast deployment

Question 31

Docker Architecture

Answer 31

Follows client-server architecture

Question 32

Docker compose

Answer 32

Build and run multi-container docker applications

Question 33

VMWare Topology

Answer 33

Architecture to create virtual data center

Question 34

VMWare components

Answer 34

VMware ESX server Virtual machine file system vCenter management server Virtual Infrastructure clients Virtual Infrastructure web access

Question 35

Distributed Services: VMWare Vmotion

Answer 35

Enables migration of virtual machines from one host memory to another without service interruption

Question 36

Distributed Services: Storage vMotion (SVMotion)

Answer 36

Does same as vMotion but also moves storage information Enables data center level VM migration