This chapter is from the book
This chapter is from the book
This chapter is from the book
Virtual Machine Images
A virtual machine image is a template for creating new instances. You can choose images from a catalog to create images or save your own images from running instances. Specialists in those platforms often create catalog images, making sure that they are created with the proper patches and that any software is installed and configured with good default settings. The images can be plain operating systems or can have software installed on them, such as databases, application servers, or other applications. Images usually remove some data related to runtime operations, such as swap data and configuration files with embedded IP addresses or host names.
Image development is becoming a larger and more specialized area. One of the outstanding features of the IBM SmartCloud Enterprise is the image asset catalog. The asset catalog stores a set of additional data about images, including a “Getting Started” page, a parameters file that specifies additional parameters needed when creating an instance, and additional files to inject into the instance at startup. It also hosts forums related to assets, to enable feedback and questions from users of images to the people who created those images. Saving your own images from running instances is easy, but making images that other people use requires more effort; the IBM SmartCloud Enterprise asset catalog provides you with tools to do this.
Because many users share clouds, the cloud helps you track information about images, such as ownership, history, and so on. The IBM SmartCloud Enterprise knows what organization you belong to when you log in. You can choose whether to keep images private, exclusively for your own use, or to share with other users in your organization. If you are an independent software vendor, you can also add your images to the public catalog.
Some differences between Linux and Windows exist. The filelike description of the Linux operating system makes it easy to prepare for virtualization. An image can be manipulated as a file system even when the instance is not running. Different files, such as a user’s public SSH key and runtime parameters, can be injected into the image before booting it. Cloud operators take advantage of this for ease of development and to make optimizations. The same method of manipulating files systems without booting the OS cannot be done in Windows.