Abstract
Cloud resources nowadays contribute an essential share of resources for computing in high-energy physics. Such resources can be either provided by private or public IaaS clouds (e.g. OpenStack, Amazon EC2, Google Compute Engine) or by volunteers computers (e.g. LHC@Home 2.0). In any case, experiments need to prepare a virtual machine image that provides the execution environment for the physics application at hand. The CernVM virtual machine since version 3 is a minimal and versatile virtual machine image capable of booting different operating systems. The virtual machine image is less than 20 megabyte in size. The actual operating system is delivered on demand by the CernVM File System. CernVM 3 has matured from a prototype to a production environment. It is used, for instance, to run LHC applications in the cloud, to tune event generators using a network of volunteer computers, and as a container for the historic Scientific Linux 5 and Scientific Linux 4 based software environments in the course of long-term data preservation efforts of the ALICE, CMS, and ALEPH experiments. We present experience and lessons learned from the use of CernVM at scale. We also provide an outlook on the upcoming developments. These developments include adding support for Scientific Linux 7, the use of container virtualization, such as provided by Docker, and the streamlining of virtual machine contextualization towards the cloud-init industry standard.
Highlights
The way computing resources are today becoming available to high-energy physics (HEP) experiments is multi-fold and changing
It provides a mean to reduce the weight of software portability activities, historically a prominent component of software maintenance work in the HEP experiments
This paper focuses in particular on the status of the new bootloader technology, which in the meantime has matured to production grade, and the future steps concerning the appliance, including support for operating system level virtualization a.k.a. containers
Summary
The way computing resources are today becoming available to high-energy physics (HEP) experiments is multi-fold and changing. At the last edition of this conference a new technology for creating the virtual appliances was introduced [2], resulting in a minimal and versatile virtual machine image capable of booting different operating systems, delivered on demand by the CernVM File System. Its purpose it collect the contextualization information (users, credentials, repositories, services, ...) and to feed it to laptop/desktop virtual machines, or to create an user data file to be used when instantiating machines on clouds. The process to create a virtual machine contextualized at the case in use starts with a minimal image, referred to as μCernVM, consisting of a Linux kernel and an init RAM disk which includes the CernVM-FS client. The choice of the 3.10 LTS kernel for μCernVM provided stability to this component, with only 5 security hotfixes required in 18 months, and proved to be suited for all the operative system templates which
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