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The prompt reconstruction of the data recorded from the Large Hadron Collider (LHC) detectors has always been addressed by dedicated resources at the CERN Tier-0. Such workloads come in spikes due to the nature of the operation of the accelerator and in special high load occasions experiments have commissioned methods to distribute (spill-over) a fraction of the load to sites outside CERN. The present work demonstrates a new way of supporting the Tier-0 environment by provisioning resources elastically for such spilled-over workflows onto the Piz Daint Supercomputer at CSCS. This is implemented using containers, tuning the existing batch scheduler and reinforcing the scratch file system, while still using standard Grid middleware. ATLAS, CMS and CSCS have jointly run selected prompt data reconstruction on up to several thousand cores on Piz Daint into a shared environment, thereby probing the viability of the CSCS high performance computer site as on demand extension of the CERN Tier-0, which could play a role in addressing the future LHC computing challenges for the high luminosity LHC.

Summary We present a methodology to enable the complete software development life cycle on Cray XC systems within a container that can hold any version of the Cray Programming Environment (CPE). The installation of the CPE inside a container facilitates many aspects of the typical HPC support and operation workloads of managing Cray XC systems such as testing new CPEs, comparing CPE performances, or keeping software built with an old CPE running on updated systems. The procedure for creating a container with a CPE inside consists of three steps: the creation of a container holding the targeted CPE, the compilation of the desired software within such containers, and the packaging of the resulting binaries, libraries, and dependencies within a second lightweight container. We showcase the methodology by fulfilling a user requirement of running a two‐year‐old version of the COSMO model built with an old CPE 16.11 on today's system.