Introduction

This book will attempt to show you how to deploy RHEL 7 systems without too much of a hassle. As this book is written with automation in mind, I will emphasize on command-line utilities rather than elaborating on its GUI counterparts, which are useless for automation.

This chapter explains how to build and manage KVM guests using the libvirt interface and various tools built around it. It will provide a brief overview on how to set up a KVM on RHEL and manage its resources. The setup provided in this overview is far from the ready enterprise as it doesn't provide any redundancy, which is generally required in enterprises. However, the recipes provided are relevant in enterprise setups as the interface stays the same. Most of the time, you will probably use a management layer (such as RHEV or oVirt), which will make your life easier in managing redundancy.

As most tasks performed need to be automated in the end, I tend not to use any graphical interfaces as these do not allow an easy conversion into script. Hence, you will not find any recipes in this chapter involving a graphical interface. These recipes will primarily focus on virsh, the libvirt management user interface that is used to manage various aspects of your KVM host and guests. While a lot of people rely on the edit option of virsh, it doesn't allow you to edit a guest's configuration in real time. Editing your guest's XML configuration in this way will require you to shut down and boot your guest for the changes to take effect. A reboot of your guest doesn't do the trick as the XML configuration needs to be completely reread by the guest's instance in order for it to apply the changes. Only a fresh boot of the guest will do this.

The virsh interface is also a shell, so by launching virsh without any commands, you will enter the libvirt management shell. A very interesting command is help. This will output all the available commands grouped by keyword. Each command accepts the --help argument to show a detailed list of the possible arguments, and their explanation, which you can use.