Now that we've looked at getting a disk image into Glance, let's investigate how a cloud image is built. A cloud image is just a sealed disk image with cloud-init included. A sealed disk image is a file that has an operating system installed in it and has had all the host-specific items removed from it. Cloud-init is a post-boot process that checks the metadata service of OpenStack and asks for post-boot commands that should be run on the launched instance. We'll see cloud-init's use cases in Chapter 6, Instance Management, and Chapter 10, Orchestration; for now, we'll just make sure it's included in the cloud image we build. To build the image, we'll use virt-install. There are quite a few other options. If you're familiar with a different disk image-building tool, use that if you like. This is just one example of how to build one of these images. Go ahead and make sure virt-install is installed. The following command accomplishes this:

build-host# yum install -y virt...