Designing a flexible and modular architecture for a private cloud: a case study

Cloud computing is an emerging paradigm used by an increasingly number of enterprises to support their business and promises to make the utility computing model fully realized by exploiting virtualization technologies. Free software is now mature not only to offer well-known server-side applications, but also to land on desktop computers. However, administering in a decentralized way a large amount of desktop computers represents a demanding issue: system updates, backups, access policies, etc. are hard tasks to be managed separately on each computer. This paper presents a general purpose architecture for building a reliable, scalable, flexible, and modular private cloud that exploits virtualization technologies at different levels. The architecture can be used to offer a variety of services that span from web applications and web services to soft real-time applications. To show the features of the proposed architecture, we also present the design and implementation over it of a Linux Terminal Server Project (LTSP) cluster that benefits from the underlying IaaS services offered by the private cloud. The cloud infrastructure, as well as the LTSP, have been implemented exclusively using free software and are now in a production state, being used by approximately 200 users for their everyday work. We hope that our description and design decisions can provide some guidance about designing an architecture for a cloud service provider.