Book Image

KVM Virtualization Cookbook

By : Konstantin Ivanov
Book Image

KVM Virtualization Cookbook

By: Konstantin Ivanov

Overview of this book

Virtualization technologies such as KVM allow for better control over the available server resources, by deploying multiple virtual instances on the same physical host, or clusters of compute resources. With KVM it is possible to run various workloads in isolation with the hypervisor layer providing better tenant isolation and higher degree of security. This book will provide a deep dive into deploying KVM virtual machines using qemu and libvirt and will demonstrate practical examples on how to run, scale, monitor, migrate and backup such instances. You will also discover real production ready recipes on deploying KVM instances with OpenStack and how to programatically manage the life cycle of KVM virtual machines using Python. You will learn numerous tips and techniques which will help you deploy & plan the KVM infrastructure. Next, you will be introduced to the working of libvirt libraries and the iPython development environment. Finally, you will be able to tune your Linux kernel for high throughput and better performance. By the end of this book, you will gain all the knowledge needed to be an expert in working with the KVM virtualization infrastructure.
Table of Contents (15 chapters)
Title Page
Credits
About the Author
About the Reviewer
www.PacktPub.com
Customer Feedback
Preface

Using pre-existing images


In the Installing a custom OS on the image with debootstrap recipe, we saw how to use the debootstrap command to install Debian on an image we built. Most Linux vendors provide already built images of their distributions for various architectures. Installable images are also available for manually installing the guest OS. In this recipe, we are going to demonstrate how to obtain and examine CentOS and Debian images that have already been built. In a later recipe, we are going to show how to start QEMU/KVM instances using those same images.

Getting ready

For this recipe, we are going to need QEMU installed on the host OS. For instructions on how to install QEMU, please refer to the Installing and configuring QEMU recipe from this chapter. We are also going to need the wget utility to download the images from the upstream public repositories.

How to do it...

To obtain Debian Wheezy images for use with QEMU and KVM, perform the following:

  1. Download the image using wget:
root@kvm:~tmp# wget https://people.debian.org/~aurel32/qemu/amd64/debian_wheezy_amd64_standard.qcow2    
--2017-03-09 22:07:20-- 2    Resolving people.debian.org (people.debian.org)... 2001:41c8:1000:21::21:30, 5.153.231.30    Connecting to people.debian.org (people.debian.org)|2001:41c8:1000:21::21:30|:443... connected.    HTTP request sent, awaiting response... 200 OK    Length: 267064832 (255M)    Saving to: ‘debian_wheezy_amd64_standard.qcow2’    debian_wheezy_amd64_standard.qcow2 100% .  [===================================>] 254.69M 35.8MB/s in 8.3s    2017-03-09 22:07:29 (30.9 MB/s) - ‘debian_wheezy_amd64_standard.qcow2’ saved [267064832/267064832]    
root@kvm:~#
  1. Inspect the type of the image:
root@kvm:~# qemu-img info debian_wheezy_amd64_standard.qcow2    
image: debian_wheezy_amd64_standard.qcow2    
file format: qcow2    
virtual size: 25G (26843545600 bytes)    
disk size: 261M    
cluster_size: 65536    
Format specific information:    
compat: 1.1    
lazy refcounts: false    
refcount bits: 16    
corrupt: false    
root@kvm:~#

To download CentOS images run the following commands:

  1. Download the image using wget:
root@kvm:/tmp# wget         https://cloud.centos.org/centos/7/images/CentOS-7-x86_64-GenericCloud.qcow2    --2017-03-09 22:11:34-- https://cloud.centos.org/centos/7/images/CentOS-7-x86_64-GenericCloud.qcow2    Resolving cloud.centos.org (cloud.centos.org)... 2604:4500::2a8a, 136.243.75.209    Connecting to cloud.centos.org (cloud.centos.org)|2604:4500::2a8a|:443... connected.    HTTP request sent, awaiting response... 200 OK    Length: 1361182720 (1.3G)    Saving to: ‘CentOS-7-x86_64-GenericCloud.qcow2’
CentOS-7-x86_64-GenericCloud.qcow2 100%[=========================================>] 1.27G 22.3MB/s in 54s
2017-03-09 22:12:29 (24.0 MB/s) - ‘CentOS-7-x86_64-GenericCloud.qcow2’ saved [1361182720/1361182720]
FINISHED --2017-03-09 22:12:29--    Total wall clock time: 54s    Downloaded: 1 files, 1.3G in 54s (24.0 MB/s)    
root@kvm:/tmp#
  1. Inspect the type of the image:
root@kvm:~# qemu-img info CentOS-7-x86_64-GenericCloud.qcow2    
image: CentOS-7-x86_64-GenericCloud.qcow2    
file format: qcow2    
virtual size: 8.0G (8589934592 bytes)    
disk size: 1.3G    
cluster_size: 65536    
Format specific information:    
compat: 0.10    
refcount bits: 16    
root@kvm:~#

How it works...

There are many public repositories on the Internet that provide images of various types, most commonly qcow2 for use with QEMU/KVM. In the previous section, we used the official CentOS repository to obtain the image and an another one containing prebuilt images for Debian.

Both images are in the qcow2 format, as we confirmed in step 2.

There's more...

So far, we've only seen how to build, examine, manipulate, and download images. In the next recipe, we are going to focus on how to actually use the images to start QEMU/KVM instances.

See also

Examine the following links to get more information about what prebuilt images are available for the listed distributions: