Cloud-computing platforms such as Amazon’s Elastic Compute Cloud (EC2), Microsoft’s Azure Services Platform, and Google App Engine have given many businesses flexible access to computing resources, ushering in an era in which, among other things, startups can operate with much lower infrastructure costs. Instead of having to buy or rent hardware, users can pay for only the processing power that they actually use and are free to use more or less as their needs change.

However, relying on cloud computing comes with drawbacks, including privacy, security, and reliability concerns. So there is now growing interest in open-source cloud-computing tools, for which the source code is freely available. These tools could let companies build and customize their own computing clouds to work alongside more powerful commercial solutions.

One open-source software-infrastructure project, called Eucalyptus, imitates the experience of using EC2 but lets users run programs on their own resources and provides a detailed view of what would otherwise be the black box of cloud-computing services.

Another open-source cloud-computing project is the University of Chicago’s Globus Nimbus, which is widely recognized as having pioneered the field. And a European cloud-computing initiative coordinated by IBM, called RESERVOIR, features several open-source components, including OpenNebula, a tool for managing the virtual machines within a cloud. Even some companies, such as Enomaly and 10gen, are developing open-source cloud-computing tools.

Rich Wolski, a professor in the computer-science department at the University of California, Santa Barbara, who directs the Eucalyptus project, says that his focus is on developing a platform that is easy to use, maintain, and modify. “We actually started from first principles to build something that looks like a cloud,” he says. “As a result, we believe that our thing is more malleable. We can modify it, we can see inside it, we can install it and maintain it in a cloud environment in a more natural way.”

Reuven Cohen, founder and chief technologist of Enomaly, explains that an open-source cloud provides useful flexibility for academics and large companies. For example, he says, a company might want to run most of its computing in a commercial cloud such as that provided by Amazon but use the same software to process sensitive data on its own machines, for added security. Alternatively, a user might want to run software on his or her own resources most of the time, but have the option to expand to a commercial service in times of high demand. In both cases, an open-source cloud-computing interface can offer that flexibility, serving as a complement to the commercial service rather than a replacement.

Indeed, Wolski says that Eucalyptus isn’t meant to be an EC2 killer (for one thing, it’s not designed to scale to the same size). However, he believes that the project can make a productive contribution by offering a simple way to customize programs for use in the cloud. Wolski says that it’s easier to assess a program’s performance when it’s possible to see how it operates both at the interface and from within a cloud.

Wolski says that Eucalyptus will also imitate Amazon’s popular Simple Storage Surface, which allows users to access storage space on demand, as well as its Elastic IP addresses, which keeps the address of Web resources the same, even if the physical location changes.

Ignacio Llorente, a professor in the distributed systems architecture group at the Universidad Complutense de Madrid, in Spain, who works on OpenNebula, says that Eucalyptus’s main advantage is that it uses the popular EC2 interface. However, he adds that “the open-source interface is only one part of the solution. Their back-end [the system's internal management of physical resources and virtual machines] is too basic. A complete cloud solution requires other components.” Llorente says that Eucalyptus is just one example of a growing ecosystem of open-source cloud-computing components.

Wolski expects many of Eucalyptus’s users to be academics interested in studying cloud-computing infrastructure. Although he doubts that such a platform would be used as a distributed system for ordinary computer users, he doesn’t discount the possibility. “You can argue it both ways,” he notes. But Wolski says that he thinks some open-source cloud-computing tool will become important in the future. “If it’s not Eucalyptus, I suspect [it will be] something else,” he says. “There will be an open-source thing that everyone gets excited about and runs in their environment.”

Copyright Technology Review 2008.