StashCache By The Numbers
The StashCache federation is comprised of 3 components: Origins, Caches, and Clients. There are additional components that increase the usability of StashCa...
In 2013, Greg Thain presented putting users in a box for job isolation. It used three technologies in order to enable the isolation:
CHROOTs - Create an isolated filesystem to protect the system from modifications.
We used these chroot in Nebraska’s transition from RHEL5 to RHEL6. But the
chroot capability has degraded over time since it is difficult to author and maintain raw
chroot, namespaces, and cgroups are all part of Docker’s containerization solution. Docker provides a very approachable way to compose and publish images. Further, we don’t need to maintain a RHEL6 image, only our local customizations on top.
We decided to use HTCondor’s new Docker universe. We want to trnasform incomping grid jobs into Docker universe jobs.
We chose Docker over Virtual Machines due to potential IO bottlenecks that have been identified in recent publications.
Our host environment consists of:
The default container is based off of CentOS 6. It includes the OSG WN packages, gcc, glibc-headers… for various system depenedencies for the CMS project. Here is the Docker Hub.
The full DockerFile is on Github and below.
FROM centos:centos6 RUN yum -y install http://repo.grid.iu.edu/osg/3.3/osg-3.3-el6-release-latest.rpm && \ yum -y install epel-release && \ yum -y install osg-wn-client osg-wn-client-glexec cvmfs && \ yum -y install glibc-headers && \ yum -y install gcc && \ yum -y install redhat-lsb-core sssd-client && \ yum clean all && \ yum -y update # Create condor user and group RUN groupadd -r condor && \ useradd -r -g condor -d /var/lib/condor -s /sbin/nologin condor # Add lcmaps.db COPY lcmaps.db /etc/lcmaps.db RUN yum -y install openssh-clients && yum clean all
That’s it, that’s all of the DockerFile.
There are a few important directories from the host that need to be available to the container - for example, the HDFS-based storage system. Docker refers to these as volume mounts. Currently, we bring in a total of 6 different directories. Most volumes are marked read only - no need for the jobs to write to these. Exception is SSSD: need to write to a Unix socket to lookup usernames.
DOCKER_VOLUME_DIR_CVMFS = /cvmfs:/cvmfs:ro DOCKER_VOLUME_DIR_ETC_CVMFS = /etc/cvmfs:/etc/cvmfs:ro DOCKER_VOLUME_DIR_HDFS = /mnt/hadoop:/mnt/hadoop:ro DOCKER_VOLUME_DIR_GRID_SECURITY = /etc/grid-security:/etc/grid-security:ro DOCKER_VOLUME_DIR_SSSD = /var/lib/sss/pipes/nss DOCKER_VOLUME_DIR_NSSWITCH = /etc/nsswitch.conf:/etc/nsswitch.conf:ro DOCKER_MOUNT_VOLUMES = CVMFS, ETC_CVMFS, HDFS, GRID_SECURITY, SSSD, NSSWITCH
The HTCondor-CE accepts jobs into the cluster from external submitters.
Snippets from the
condor_job_router transform language
Cmd needs to be prepended with
copy_Cmd = "orig_Cmd" eval_set_Cmd = ifThenElse(regexp("^/", orig_Cmd), orig_Cmd, strcat("./",orig_Cmd))
DockerImage needs to be set:
copy_DockerImage = "orig_DockerImage" eval_set_DockerImage = ifThenElse(isUndefined(orig_DockerImage), “unlhcc/osg-wn-el6", orig_DockerImage)
Running Production CMS and OSG jobs on Nebraska’s CMS Tier 2. Currently ~10% of the Nebraska Tier 2 is Docker-enabled. Will be expanding to the entire cluster in the coming weeks: goal is to be done by the end-of-summer. Next step is to further explore how to (safely) expose this capability to OSG VOs and users.
HTCondor treats all Docker images the same. We want to differentiate the images that come from the “good guys” (us) versus the “bad guys” (users). Still uncomfortable with the idea of allowing users to request arbitrary images. RHEL7.2 includes various sandboxing mechanisms: there’s no (publicly) known ways to break out, but the track record is relatively poor.
Things that would simplify our setup: