Integration of NEMO into an existing particle physics environment through virtualization

With the ever-growing amount of data collected with the experiments at the Large Hadron Collider (LHC) (Evans et al., 2008), the need for computing resources that can handle the analysis of this data is also rapidly increasing. This increase will even be amplified after upgrading to the High Luminosity LHC (Apollinari et al., 2017). High-Performance Computing (HPC) and other cluster computing resources provided by universities can be useful supplements to the resources dedicated to the experiment as part of the Worldwide LHC Computing Grid (WLCG) (Eck et al., 2005) for data analysis and production of simulated event samples. Computing resources in the WLCG are structured in four layers – so-called Tiers. The first layer comprises two Tier-0 computing centres located at CERN in Geneva, Switzerland and at the Wigner Research Centre for Physics in Budapest, Hungary. The second layer consists of thirteen Tier-1 centres, followed by 160 Tier-2 sites, which are typically universities and other scientific institutes. The final layer are Tier-3 sites which are directly used by local users. The University of Freiburg is operating a combined Tier-2/Tier-3, the ATLAS-BFG (Backofen et al., 2006). The shared HPC cluster »NEMO« at the University of Freiburg has been made available to local ATLAS (Aad et al., 2008) users through the provisioning of virtual machines incorporating the ATLAS software environment analogously to the bare metal system at the Tier-3. In addition to the provisioning of the virtual environment, the on-demand integration of these resources into the Tier-3 scheduler in a dynamic way is described. In order to provide the external NEMO resources to the user in a transparent way, an intermediate layer connecting the two batch systems is put into place. This resource scheduler monitors requirements on the user-facing system and requests resources on the backend-system