Developing and Hosting Applications on the Cloud (Shawn Kahl's Library) by Alex Amies & Harm Sluiman & Qiang Guo Tong & Guo Ning Liu

Author:Alex Amies & Harm Sluiman & Qiang Guo Tong & Guo Ning Liu
Language: eng
Format: epub
Publisher: IBM Press
Published: 2012-08-22T04:00:00+00:00

Figure 6.1. Files included with the IBM Rational Team Concert image catalog entry

Parameters passed into the image at creation time will be passed into the instance and will be available under /etc/cloud/parameters.xml. A basic image with no parameters passed in at instance creation time has a simple parameters.xml file that looks like this:

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<?xml version=”1.0” encoding=”UTF-8” standalone=”yes”?>

<parameters>

<firewall>

<rule>

<source>0.0.0.0/0</source>

<minport>1</minport>

<maxport>65535</maxport>

</rule>

</firewall>

</parameters>

This contains firewall data for iptables.

The Linux operating system provides startup customization integration points using scripts in the init.d directory, which are linked to the rc.d directories for each of the Linux run levels. The scripts also act as interfaces to services, allowing management by a system administrator. The Red Hat base images contain scripts /etc/init.d/cloud-startup3.sh and /etc/init.d/cloud-startup5.sh that can be used to provide integration points for startup customization. The SUSE Linux Enterprise images have similar scripts. Windows customization and startup is different because Windows virtual machine images cannot be manipulated as open file systems.

The file scripts.txt, stored in the image catalog entry in Rational Asset Manager (RAM), is a special file that stores name-value pairs of files that are copied to the instance during provisioning. The name is the name of the file in RAM, and the value is the target location for the file to be placed on the instance after provisioning. Consider the contents of scripts.txt for the IBM Rational Team Concert image:

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rtcsvc=/etc/init.d/cloud-startup3.sh

See the paper “Creating and Customizing Images” [Goodman, 2009] for more on images on the IBM SmartCloud Enterprise. The paper describes a simple cloud storage application based on an NFS server. It uses a Perl script to extract location and permission data supplied by the end user at provisioning time to configure the NFS server. Perl is a good choice of language to do this for Linux operating system features because it is lightweight and present with the Linux images provided on IBM SmartCloud Enterprise.

A cloud virtual machine image is not the same as a snapshot of a virtual machine. An image is intended to be portable and to be reused. A snapshot is intended as a backup of a virtual machine and includes runtime data. To our knowledge, no public clouds support snapshots in this sense. However, the concept is demonstrated by VMWare virtualization products that enable you to save a snapshot of a virtual machine. Multiple snapshots are related to each other, and only incremental data is saved, resulting in storage and performance efficiency. In VMWare terminology, a virtual machine image is called a template.

When creating an image to share with others, make sure that you clean up all logs on the system. Otherwise, you will be sharing log information with people who use your image.

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