HCW 2014 Keynote Talk.

Funded by the US National Science Foundation, the Extreme Science and Engineering Discovery Environment (XSEDE) project seeks to provide "a single virtual system that scientists can use to interactively share computing resources, data and experience."1 The resources, owned by many different organizations and individuals in the US or abroad, may be at national centers, on campuses, in individual research labs, or at home. Heterogeneity pervades such an environment. There are heterogeneous processor architectures, node architectures, operating systems, load management systems, file systems, linkage libraries, MPI implementations and versions, authentication policies, authorization requirements, internet access policies and mechanisms, and operational policies, tolerance for risk -- the list goes on and on. It is the role of the XSEDE architecture to provide a clean model for component/component interactions, the definition of the standard core components, and the architectural approach to the non-functional aspects, often called the "ilities". These interfaces and interaction patterns must be sufficient to implement the XSEDE use case both today and into the future. We have followed the principles that Notkin and others espoused in the early 1990s.This talk describes the architectural features required to satisfy one of the most demanding use cases: executing workflows spanning XSEDE resources and campus-based resources. This use highlights the obvious functional aspects of execution and data management, identity federation, identity delegation, as well as more difficult-to-homogenize qualities such as local operational policies. We will begin with a discussion of the use case requirements, then examine how the architectural components are combined to realize the use case. We will then discuss some of the problems encountered along the way both with the standards used as well as the approach of a homogeneous virtual machine.