Abstract

This paper describes the deployment of the offline software of the ATLAS experiment at LHC in containers for use in production workflows such as simulation and reconstruction. To achieve this goal we are using Docker and Singularity, which are both lightweight virtualization technologies that can encapsulate software packages inside complete file systems. The deployment of offline releases via containers removes the interdependence between the runtime environment needed for job execution and the configuration of the computing nodes at the sites. Docker or Singularity would provide a uniform runtime environment for the grid, HPCs and for a variety of opportunistic resources. Additionally, releases may be supplemented with a detector’s conditions data, thus removing the need for network connectivity at computing nodes, which is normally quite restricted for HPCs. In preparation to achieve this goal, we have built Docker and Singularity images containing single full releases of ATLAS software for running detector simulation and reconstruction jobs in runtime environments without a network connection. Unlike similar efforts to produce containers by packing all possible dependencies of every possible workflow into heavy images (≈ 200GB), our approach is to include only what is needed for specific workflows and to manage dependencies efficiently via software package managers. This approach leads to more stable packaged releases where the dependencies are clear and the resulting images have more portable sizes ( 16GB). In an effort to cover a wider variety of workflows, we are deploying images that can be used in raw data reconstruction. This is particularly challenging due to the high database resource consumption during the access to the experiment’s conditions payload when processing data. We describe here a prototype pipeline in which images are provisioned only with the conditions payload necessary to satisfy the jobs’ requirements. This database-on-demand approach would keep images slim, portable and capable of supporting various workflows in a standalone fashion in environments with no network connectivity.

Highlights

  • Docker is a light weight, software based virtualization technology [1], which encapsulates a piece of software inside a complete file system containing everything that the applications will need to run: code, runtime, system tools, system libraries, etc

  • This paper describes the deployment of the offline software of the ATLAS experiment at Large Hadron Collider (LHC) in containers for use in production workflows such as simulation and reconstruction

  • In addition to the standalone images for simulation we build images for digitization and reconstruction workflows. In this case the conditions database is prepared by copying COOL folders [5] from a central conditions Oracle database to a SQLite file, which is packaged in the images. This SQLite database file has the minimal payload necessary to execute a reconstruction job, specified by performing a folder dump of the COOL folders that are required to process the input data based on its metadata, such as the run number range and/or the time interval, which specify data taking periods

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Summary

ATLAS software in Docker images

The ATLAS Offline Software Group currently hosts a fairly comprehensive body of documentation with detailed instructions for building, running and managing containers with ATLAS software [3]. In addition to the standalone images for simulation we build images for digitization and reconstruction workflows In this case the conditions database is prepared by copying COOL folders [5] from a central conditions Oracle database to a SQLite file, which is packaged in the images. A similar procedure is followed to build images for raw data reconstruction; these images are not completely standalone as there are currently no ATLAS tools available for copying from the online trigger menu database to an SQLite file. For this reason, performance tests on images used for data reconstruction require a network connection to this Oracle database. Execute: docker pull atlas/athena:21.0.15_100.0.2 # detector simulation docker pull atlas/athena:21.0.23_DBRelease-200.0.1 # digi+reconstruction docker pull atlas/athena:21.0.50_200.0.1 # data reconstruction

Performance of containers running ATLAS software
Real data reconstruction
Full Text
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