Rolls: modifying a standard system installer to support user-customizable cluster frontend appliances

The Rocks toolkit uses a graph-based framework to describe the configuration of all node types (termed appliances) that make up a complete cluster. With hundreds of deployed clusters, our turnkey systems approach has shown to be quite easily adapted to different hardware and logical node configurations. However, the Rocks architecture and implementation contains a significant asymmetry: the graph definition of all appliance types except the initial frontend can be modified and extended by the end-user before installation. However, frontends can be modified only afterward by hands-on system administration. To address this administrative discontinuity between nodes and frontends, we describe the design and implementation of Rolls. First and foremost, Rolls provide both the architecture and mechanisms that enable the end-user to incrementally and programmatically modify the graph description for all appliance types. New functionality can be added and any Rocks-supplied software component can be overwritten or removed simply by inserting the desired Roll CD(s) at installation time. This symmetric approach to cluster construction has allowed us to shrink the core of the Rocks implementation while increasing flexibility for the end-user. Rolls are optional, automatically configured, cluster-aware software systems. Current add-ons include: scheduling systems (SGE, PBS), grid support (based on NSF Middleware Initiative), database support (DB2), Condor, integrity checking (Tripwire) and the Intel compiler. Community-specific Rolls can be and are developed by groups outside of the Rocks core development group.