HyperV interview questions

• HyperV  interview questions

Server Virtualization:
Server Virtualization enables multiple operating systems can run on a single hosting server.
In Server virtualization, physical server resources are abstracted logically to create and run virtual machines. (ESXi, KVM, Hyper-V).

Storage Virtualization:
Storage virtualization enables grouping of multiple physical storage disks into single logical storage and it will be presented as single storage to all the servers. VMware vSAN is the best example of storage virtualization.

Network Virtualization:
Network Virtualization allows making a complete software-defined network (SDN) by decoupling the virtual network from the underlying network resources. Network virtualization is the process of combining hardware network resources and software network resources in a single software-based administrative entity.

Desktop Virtualization:
It enables to deploy multiple desktops on few server hardware and accessed by users from any location. VMware Horizon View is the best example for desktop virtualization.

Application Virtualization:
Application virtualization enables to use of the application anywhere without installing the software our device.

What is Type 1 Hypervisor?
Type 1 is called as bare metal Hypervisor which directly installed on physical servers. It offers high-performance and lower resource usage. Example: VMware ESXi, Xen Servers, Hyper-V

What is Type 2 Hypervisor?
Type 2 is called as Hosted Hypervisor which runs on top of operating systems. This type of hypervisor will be installed as an application. It offers moderate performance. But it’s very easy to setup and manages the environment. Example: VMware Workstation, Oracle Virtual Box.

https://www.unixarena.com/2019/08/virtualization-hypervisor-basic-interview-questions.html/

VMware Interview Questions

• VMware Interview Questions

Explain what is hypervisor
A hypervisor is a program that enables multiple operating systems to share a single hardware host.
The hypervisor controls the resources and host processor, allocating what is required for each operating system in turn and make sure that the guest operating system cannot disrupt each other.

Explain VMware DRS?
VMware DRS stands for Distributed Resource Scheduler; it dynamically balances resources across various host under a cluster or resource pool.

Define the term ’VMKenel’.
VMWare Kernel is a proprietary kernel of VMware. It needs an operating system to boot and manage the kernel. A service console is being offered whenever VMWare kernel is booted.

 What is the use of Promiscuous Mode?
Promiscuous mode is useful when you want to run a virtual machine with network sniffers helps you to capture packet of that network. Moreover, if the promiscuous mode set to accept, all the communication is visible to all the virtual machines.

What is Cold and Hot Migration?
When you migrate powered off or suspended, it is known as cold migration. When you migrate your running power on virtual machines, it is known as hot migration.

What is Virtual Desktop Infrastructure?
Virtual Desktop Infrastructure which also known as VDI allows you to host the desktop operating system on the centralized window server in a data center. It is also known as server-based computing as it is the variation on the client-server computing model.

Explain the importance of snapshot in VMWare
A VMWare snapshot is a copy of a virtual machine disk file which is used to restore a VM to a specific point in time when the system fails, or system error occurs.

What is VVol?
Virtual Volume known as VVol is a new VM disk management feature concept introduced in vSphere 6.0. It enables array-based operation at the virtual disk level.  It is automatically created when a virtual disk is created in a virtual environment.

Can we do vMotion between two data centers?
Yes, we can do vMotion between two datacenters. However,  for this VM should be powered off.

What is RDM?
RDM is a sort form of Raw Device Mapping. It is a file stored in VMFS volume which acts as a proxy for a raw physical device. It allows you to store virtual machine data directly on LUN.

What is NFS?
NFS is a Network file system. It is a file sharing protocol which ESXI host used to communicate with the NAS device. It is a specialized store device which connects to a network and can provide file aces service to ESXI hosts.

https://career.guru99.com/top-15-vmware-interview-questions/

• Explain what happens to a Virtual Machine after the host which it is running on, fails.

First, you should explain that the VM is forcefully powered off.
Next, ask if the host was in a correctly configured HA cluster (If it isn’t then nothing else happens to the VM)
If the Host is HA enabled, then ask what the Virtual Machine restart policy is. If it’s disabled then the VM will not be restarted on other hosts.
Ignoring the HA master election process, the simple answer is that the Virtual Machine will be rebooted on another ESXi host in the cluster.
Mention that there are things that will stop a Virtual Machine from being restarted on other hosts such as Admission Control settings & resource availability on the host.
The key thing to remember is that HA does NOT trigger a vMotion.

When should Promiscuous Mode be enabled on a Virtual Switch

Promiscuous Mode is a vSwitch and Portgroup setting that allows for Virtual Machines to receive all traffic within the same vSwitch or Portgoup (depending on where you set the configuration)
Typical use cases for this are packet sniffing applications.

Name 3 benefits of installing VMware Tools on Virtual Machines

Enables features such as Guest Introspection for NSX / agentless antivirus
Installs the VMXNET3 driver for improved network performance.
Allows the ability to copy and paste between the VM and desktop (some other settings might need to be enabled first)

What techniques are available to ESXi to reclaim memory?

Transparent Page Sharing (TPS) – Note that as of vSphere 6.0, this is disabled by default.
Ballooning – Requests VMware tools to “inflate a memory balloon” inside the VM until excess memory is released back to ESXi.
Memory Compression.
Swapping – This is the last option that ESXi will use to reclaim memory because it is the most disruptive to performance as memory gets swapped out from real memory onto disk

What is the impact of using Thick Eager Zeroed disk provisioning for VMDKs?
This disk type will zero out all data on the disk before allocating the VMDK to the Virtual Machine.
This has some performance benefit to the VM because it doesn’t have to zero a block before it can be written to.
The negative side is that it takes longer to provision the VMDK to the VM (since it has to zero all blocks first) and it has a measurable, sustained IO hit on the storage system

What are the main benefits of a Distributed Switch?
    Central Management of all ESXi host’s networking, meaning that there is only one switch to manage rather than one per host.
    The ability to enable Network IO Control (NIOC)
    NetFlow support.

Name 3 Virtual Machine Files

    VMX – The Virtual Machine configuration file
    NVRAM – The VM’s BIOS file
    VMEM – The VM’s pagefile
    VMSD – VM Snapshot state file


https://virtualg.uk/10-vmware-interview-questions-and-answers/

Linux Virtual Server (LVS)

• The LVS cluster system is also known as load balancing server cluster.

Build a high-performance and highly available server for Linux using clustering technology, which provides good scalability, reliability and serviceability.
http://www.linuxvirtualserver.org/whatis.html

• TCPHA

TCPHA is a subproject of LVS.
TCPHA can be used to build a high performance and high available server based on a cluster of Linux servers.

TCPHA implements an architecture for scalable content-aware request distribution in cluster-base servers. It implements Kernel Layer-7 switching based on TCP Handoff for the Linux operating system. Since the overhead of layer-7 switching in user-space is very high, it is good to implement it inside the kernel in order to avoid the overhead of context switching and memory copying between user-space and kernel-space, furthermore, the responses are sent directly to clients, not passing the dispatcher, which will greatly improve the performance of cluster.

TCPHA, inspired by KTCPVS and IPVS, merges their strongpoints. Otherwise, the installation and configuration are very simple.

http://dragon.linux-vs.org/~dragonfly/htm/tcpha.htm

• The goal of Linux Virtual Server (LVS) is to provide a basic framework that directs network connections to multiple servers that share their workload.

Linux Virtual Server is a cluster of servers (one or more load balancers and several real servers for running services) which appears to be one large, fast server to an outside client.
This apparent single server is called a virtual server.

The real servers and the load balancers may be interconnected by either high-speed LAN or by geographically dispersed WAN. The load balancers can dispatch requests to the different servers. They make parallel services of the cluster appear as a virtual service on a single IP address (the virtual IP address or VIP). Request dispatching can use IP load balancing technologies or application-level load balancing technologies. Scalability of the system is achieved by transparently adding or removing nodes in the cluster. High availability is provided by detecting node or daemon failures and reconfiguring the system appropriately.
https://www.suse.com/documentation/sle_ha/book_sleha/data/cha_ha_lvs.html

• TCP Splicing

TCPSP implements tcp splicing for the Linux kernel. The tcp splicing is a technique to splice two connections inside the kernel, so that data relaying between the two connections can be run at near router speeds. This technique can be used to speed up layer-7 switching, web proxy and application firewall running in the user space.
TCPSP is released as a small software component of the Linux Virtual Server project.
http://www.linuxvirtualserver.org/software/tcpsp/index.html

• Job Scheduling Algorithms in Linux Virtual Server

    Round-Robin Scheduling
    Weighted Round-Robin Scheduling
    Least-Connection Scheduling
    Weighted Least-Connection Scheduling
    Locality-Based Least-Connection Scheduling
    Locality-Based Least-Connection with Replication Scheduling
    Destination Hashing Scheduling
    Source Hashing Scheduling
    Shortest Expected Delay Scheduling
    Never Queue Scheduling

http://www.linuxvirtualserver.org/docs/scheduling.html

vbox networking

NAT - Your host will act as a router (firewall) and your guests will be on a private subnet. Use this if you are not running servers on the guests.

Bridged - Your guests will get a ip address on the same subnet as your host.

Internal networking

    This can be used to create a different kind of software-based network which is visible to selected virtual machines, but not to applications running on the host or to the outside world.
Host-only networking

    This can be used to create a network containing the host and a set of virtual machines, without the need for the host's physical network interface. Instead, a virtual network interface (similar to a loopback interface) is created on the host, providing connectivity among virtual machines and the host.
   

convert VMware to VirtualBox

• VMware to VirtualBox

Before migrating a virtual machine from VMware to VirtualBox, ensure it’s “powered off” in VMware – not suspended.
browse to the OVFTool folder. If you’re using VMware Player, you’ll find it at C:\Program Files (x86)\VMware\VMware Player\OVFTool
https://www.howtogeek.com/125640/how-to-convert-virtual-machines-between-virtualbox-and-vmware/

VM Player vs VMware Workstation

• Workstation has some features that Player lacks, such as teams (groups of VMs connected by private LAN segments) and multi-level snapshot trees. It's aimed at power users and developers; they even have some hooks for using a debugger on the host to debug code in the VM (including kernel-level stuff). The core technology is the same, though.

VMware Workstation is much more advanced and comes with powerful features including snapshots, cloning, remote connections to vSphere, sharing VMs, advanced Virtual Machines settings and much more. Workstation is designed to be used by technical professionals such as developers, quality assurance engineers, systems engineers, IT administrators, technical support representatives, trainers, etc
https://stackoverflow.com/questions/4170600/vmware-player-vs-vmware-workstation

• VMware Player enables you to quickly and easily create and run virtual machines. However, VMware Player lacks many powerful features, remote connections to vSphere, drag and drop upload to vSphere, multiple Snapshots and Clones, and much more.

https://www.vmware.com/products/player/faqs.html

Virtualization Security

• Microsoft fixes Hyper-V bug in Windows

Guests on a Hyper-V system could trigger the flaw in the CPU chip set to issue instructions that could place the host system into a nonresponsive state, resulting in a denial-of-service condition for guest operating systems. The attacker would have to first secure kernel-mode code execution privileges on the guest operating system in order to trigger this denial-of-service condition.
Unlike Xen and VMware, Hyper-V functions only on systems with hardware support for virtualization, such as servers with Intel VT-x and AMD-V hardware virtualization extensions. As a result, Hyper-V is typically not at risk for escape attacks, where the attackers target the guest system in order to compromise the host.
http://www.infoworld.com/article/3005238/security/microsoft-fixes-hyper-v-bug-in-windows.html

• Common Virtualization Vulnerabilities and How to Mitigate Risks

VM escape:A guest OS escapes from its VM encapsulation to interact directly with the hypervisor.This gives the attacker access to all VMs and, if guest privileges are high enough, the host machine as well. Although few if any instances are known, experts consider VM escape to be the most serious threat to VM security.

How to Mitigate Risk
VM traffic monitoring:The ability to monitor VM backbone network traffic is critical.Conventional methods will not detect VM traffic because it is controlled by internal soft switches.However, hypervisors have effective monitoring tools that should be enabled and tested.
https://pentestlab.wordpress.com/2013/02/25/common-virtualization-vulnerabilities-and-how-to-mitigate-risks/

• Top Virtualization Security Mistakes (and How to Avoid Them)

Mistake #1: Misconfiguring virtual hosting platforms, guests, and networks
Mistake #2: Failure to properly separate duties and deploy least privilege controls
Mistake #3: Failure to integrate into change/lifecycle management
Mistake #4: Failure to educate other groups, particularly risk management and compliance staff 
Mistake #5: Lack of availability or integration with existing tools and policies
Mistake #6: Lack VM visibility across the enterprise
Mistake #7: Failure to work with an open ecosystem
Mistake #8: Failure to coordinate policy between virtual machines and network connections   
Mistake #9: Failure to consider hidden costs
Mistake #10: Failure to consider user-installed VMs
https://www.sans.org/reading-room/whitepapers/analyst/top-virtualization-security-mistakes-and-avoid-them-34800

• Kernel exploits

Unlike in a VM, the kernel is shared among all containers and the host, magnifying the importance of any vulnerabilities present in the kernel. Should a container cause a kernel panic, it will take down the whole host. In VMs, the situation is much better: an attacker would have to route an attack through both the VM kernel and the hypervisor before being able to touch the host kernel.
Denial-of-service attacks
If one container can monopolize access to certain resources–including memory and more esoteric resources such as user IDs (UIDs)—it can starve out other containers on the host, resulting in a denial-of-service (DoS), whereby legitimate users are unable to access part or all of the system.
Container breakouts
By default, users are not namespaced, so any process that breaks out of the container will have the same privileges on the host as it did in the container; if you were root in the container, you will be root on the host.2 This also means that you need to worry about potential privilege escalation attacks–whereby a user gains elevated privileges such as those of the root user, often through a bug in application code that needs to run with extra privileges.
Poisoned images
If an attacker can trick you into running his image, both the host and your data are at risk. Similarly, you want to be sure that the images you are running are up-to-date and do not contain versions of software with known vulnerabilities.
https://www.oreilly.com/ideas/five-security-concerns-when-using-docker

Plop Boot Manager

• How To Boot From Live USB in VMware Player/VirtualBox - Ubuntu/Linux Mint

a way for making VirtualBox or VMware Player boot from live USB devices since this feature hasn't been implemented yet natively in both software. The trick we will use will rely on the Plop boot manager which allows via a live iso to boot from USB devices.
http://www.upubuntu.com/2012/11/how-to-boot-from-live-usb-in-vmware.html

• Plop Boot Manager 5.0 - Download

https://www.plop.at/en/bootmanager/download.html

JVM (Java Virtual Machine) vs CLR (Common Language Runtime)

We present empirical evidence to demonstrate that there is
little or no difference between the Java Virtual Machine and
the .NET Common Language Runtime, as regards the compilation
and execution of object-oriented programs

The JVM . . .
• is stack-based
• is secure—type safety is guaranteed by preventing explicit
pointer manipulation
• has automatic memory management (garbage collection)
• is object-oriented, with primitive instructions for creating
objects, accessing object members

https://www.cs.utah.edu/~asbill/jsinger.pdf

• Application virtualization software refers to both application virtual machines and software responsible for implementing them. Application virtual machines are typically used to allow application bytecode to run portably on many different computer architectures and operating systems. The application is usually run on the computer using an interpreter or just-in-time compilation (JIT).

https://en.wikipedia.org/wiki/Comparison_of_application_virtualization_software