[LINUX] LPIC304 virtualization memo
Introduction
I took the Lpic304 exam, so I made a note about server virtualization.
What is server virtualization?
https://www.kagoya.jp/howto/rentalserver/virtualization/
Operate multiple virtual servers (virtual servers) on one physical server
Software for virtualizing servers is called virtualization software, VMM, virtual machine monitor, etc.
- Disadvantages of virtualization --Performance deterioration is likely to occur. Especially network, storage IO --Security issues specific to virtual environments, etc.
Virtualization techniques
- Host OS type
- VMware Workstation
- VirutalBox
- Hypervisor type - Vmware Esxi - Xen/XenServer - HyperV
- Container type
- OpenVZ (RedHat)
- LXC
- Docker
Types of virtualization-paravirtualized and fully virtualized-
- Paravirtualized --Need to modify guest OS -** Rewrite hardware-controlled system calls to hypervisor calls ** --Application in virtual machine-> System call-> Virtual HA in virtual machine-> Hypervisor call-> Hypervisor-> Control hardware --Therefore, Windows that cannot be modified cannot be used.
- Full virtualization --Hardware emulation with virtual hardware. Reproduce hardware with software --Virtual machine-> System call (virtual CPU instruction)-> QEMU or CPU virtual support function-> Convert to actual CPU instruction -** Since it is not necessary to rewrite the system call to the hypervisor call, there is no need to modify the guest OS. ** **
Hypervisor type Xen and KVM
Features of Xen
- Supports both paravirtualization and full virtualization --For full virtualization, use the CPU virtualization support function
- Guest OS is called domain
- Use Xen with xl command, virsh, libvirt using Libxenlight (Xen's library)
KVM
- Supports full virtualization. Windows is also available
- Full virtualization, so hardware emulation is used. Qemu is used.
- KVM depends on QEMU.
- One QEMU process supports one virtual machine. Acts as a user process.
- QEMU interacts with KVM via / dev / kvm
- Use QEMU for memory and disk IO. For the CPU, use the virtualization support function.
- Convert to virtual machine-> virtual CPU instruction-> QEMU-> actual CPU instruction
- Requires KVM.ko kernel module
Manage and operate KVM
Basically, use the virsh command via libvirt (described later). However, there are other commands that can be operated.
- Create and convert virtual disks, snapshots, etc.
- qemu-img
- Take a snapshot
- kvm-img
- Directly manage and operate KVM - qemu-kvm
QEMU operation
- QEMU monitor. A virtual console provided by QEMU.
- Ctr-Alt-2
KVM storage
- Files and block devices on the host OS side can be shown to virtual machines as storage devices.
- ** Hook the IO request from the guest OS with KVM, receive it with the emulator supported by the QEMU process, and then convert it to read / write to a file or block device according to the format **
- ** From the guest OS, it can be shown to IDE, SCSI, virtio and many other types of devices via QEMU. ** **
- virtio is the fastest. By specifying the virtual disk as a virtio device and installing the virtio driver in the guest OS, you can install the virtio device.
Storage backend
There are two types: block devices and regular files. For block devices, use those on NFS or LUN
What is a block device? https://xtech.nikkei.com/it/article/Keyword/20081023/317625/
- Partitions, logical volumes, etc.
- Specifically, all disk devices such as hard disks, CD-ROM drives, and floppy disks are block devices.
file format
･ Raw
- As the name "raw" (meaning raw data) suggests, it is a file consisting of a simple column of data. It is equivalent to copying the block device with the dd command.
- Since the entity is created as a sparse file (*), it has the characteristic that it is easy for travel to occur by securing a block each time a write to a virtual disk occurs.
(*) Sparse file ... Instead of allocating the data for the file size to the disk, it is an apparent file that has only the metadata (file information). Therefore, it is possible to create a file that exceeds the disk capacity.
･ Qcow2 qcow2 is an abbreviation of "QEMU Copy On Write version2", which has the same function as a sparse file for an environment (Windows, etc.) where a sparse file cannot be used originally. It has a feature that it has metadata in the file and can collect snapshots.
The raw format does not support the snapshot function. However, by converting the file format of the virtual disk image to qcow2 with qemu-img convert, you can use the snapshot function without recreating the virtual machine.
KVM networking
- The virtual environment network is managed using libvirt's libvirtd daemon.
- By default, virbr0 (virtual bridge) and vnet (tap device) are created
tap device and virtual bridge
- The tap device is a pseudo Ethernet device that can send and receive from a user-space program. Linux kernel features
- libvirt only supports this method
- By connecting a virtual ethernet device with a tap device with a virtual bridge, the virtual machine can communicate with the real device and other virtual machines.
Method https://qiita.com/hot_study_man/items/52af652d7b20a8a998b6
- How to connect a virtual machine to a virtual bridge in NAT using iptables of the host OS (default)
- How to connect a virtual NIC to a virtual bridge to which a real NIC is connected
What is libvirt
https://www.atmarkit.co.jp/ait/articles/1011/04/news121.html
- A common interface for operating and managing virtual environments running on Linux. A library for providing a stable C language API
- Mainly Redhat
Supported VMs
Xen Hypervisor http://www.xen.org
Qemu Machine Emulator http://www.qemu.org
KVM（Kernel-based Virtual Machine） http://www.linux-kvm.org
LXC（LinuX Containers） http://lxc.sourceforge.net
UML（User Mode Linux） http://user-mode-linux.sourceforge.net
OpenVZ http://www.openvz.org
VMWare ESX http://www.vmware.com
VirtualBox
wikipedia https://ja.wikipedia.org/wiki/Libvirt
libvirtd daemon
libvirtd allows remote as well as local access. You can also manage VMs remotely with libvirtd.
Various commands of KVM
https://ping-t.com/
After creating a virtual disk image with the qemu-img command, install the OS on the disk image using the qemu-kvm command and start the virtual machine.
Example) Set the virtual disk image "vm1.img" as a hard disk and start the virtual machine using the user mode network. qemu-kvm -hda vm1.img -net nic -net user
- "-Net nic" and "-net user" can be omitted because they are default values.
OS installation Example) Set the virtual disk image "vm1.img" as a hard disk and perform OS installation using the ISO file "centos.iso".
qemu-kvm -hda vm1.img -cdrom centos.iso
Example) Set the virtual disk image "vm1.img" as a hard disk and start the virtual machine directly. qemu-kvm -hda vm1.img -kernel /boot/bzImage -initrd /boot/initramfs.img -append "root=/dev/hda"
When booting directly from the Linux kernel, you need to specify the root file system in the -append option.
The qemu-kvm command is for the host OS It can also be booted by loading the Linux kernel and initial ramdisk directly into the virtual machine. Three options are available: "-kernel", "-initrd", and "-append"
qemu-img command
qemu-img(kvm-img)
- A command to create / modify virtual disk images for KVM and manage virtual machine snapshots.
- You can also convert the file format of the virtual disk image.
qemu-img create qemu-img convert qemu-img resize qemu-img info qemu-img snapshot
1) qemu-Create a virtual disk image with the img command
Example)Format:qcow2, disk capacity:2GB, file name "centos".Create a disk image with "img"
qemu-img create -f qcow2 centos.img 2G
qemu-img create1 -f raw2 /images/sles11/hda3 8G4
2)qemu-Install the guest OS in the prepared virtual disk image with the kvm command.
Example)Virtual disk image "centos.With "img" as the hard disk, memory 1024MB, OS installation medium "centos".Start the virtual machine by specifying "iso"
qemu-kvm -hda centos.img -cdrom centos.iso -boot once=d -m 1024
convert
Convert raw to qcow2
qemu-img convert raw.img -O qcow2 QC2.img
resize
qemu-img resize hdd.img +5G
info
qemu-img info
snapshot
qemu-img snapshot -l hdd.img
qemu-kvm command
https://manual.geeko.jp/ja/cha.qemu.running.html
After creating the image, use qemu-kvm to configure the virtual machine and boot the installation system.
qemu-kvm -name "sles11"1 -M pc-0.122 -m 7683 \
-smp 24 -boot d5 \
-drive file=/images/sles11/hda,if=virtio,index=0,media=disk,format=raw6 \
-drive file=/isos/SLES-11-SP1-DVD-x86_64-GM-DVD1.iso,index=1,media=cdrom7 \
-net nic,model=virtio,macaddr=52:54:00:05:11:118 \
-vga cirrus9 -balloon virtio10
System boot after this is done
After installing the guest operating system, you no longer need to specify the CD-ROM device and you can easily boot the system:
qemu-kvm -name "sles11" -M pc-0.12 -m 768
-smp 2 -boot c
-drive file=/images/sles11/hda,if=virtio,index=0,media=disk,format=raw
-net nic,model=virtio,macaddr=52:54:00:05:11:11
-vga cirrus -balloon virtio
Supplement
The device specified in the qemu-kvm command is emulated by QEMU as an IDE device "ideN-hdN" or "ideN-cdN". The correspondence is as follows: Block device: qemu-kvm command option specification ide0-hd0/ide0-cd0 : -hda,| -drive |index=0 ide0-hd1/ide0-cd1 : -hdb,|-drive| index=1 ide1-hd0/ide1-cd0 : -hdc,|-drive| index=2, | -cdrom ide1-hd1/ide1-cd1 : -hdd,|-drive| index=3
How to get a snapshot with KVM
- virsh comment
Create Example) Create a snapshot of the virtual machine "Fedora" with the name "snapshot1"
virsh snapshot-create-as Fedora snapshot1
restore Example) Restore the virtual machine "Fedora" to the snapshot "snapshot1"
virsh snapshot-revert Fedora snapshot1
- How to use the QEMU monitor command "savevm" ・ List info snapshots
･ Create a snapshot Example) Create a snapshot
(qemu) savevm
･ Snapshot restoration Example) Restore to ID3 of snapshot
(qemu) loadvm 3
- How to use the qemu-img command
･ Create a snapshot Example) Create a snapshot of the virtual disk image "cent6.img" with the name "snapshot2".
qemu-img snapshot -c snapshot2 cent6.img
･ Snapshot restoration Example) Restore the virtual disk image "cent6.img" to the snapshot "snapshot2"
qemu-img snapshot -a snapshot2 cent6.img
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