Support CVMFS and Singularity when none of the 2 is available on the worker node
Sometimes CVMFS is not available and Singularity neither.
The Glidein should be able to connect to CVMFS and start Singularity from there.
There are some possibility, from Dave:
1. mountrepo/umountrepo only • requires fusermount; mounts in user space • map /cvmfs in container with singularity –bind (not run from cvmfs because of path) 2. cvmfsexec on RHEL 7.6 or 7.7 • requires fusermount and additionally unprivileged user namespaces enabled • maps /cvmfs without singularity, can run singularity under it • unmounts repos on exit, but not with kill -9 3. cvmfsexec on RHEL >= 7.8 • no fusermount needed, and cleans up mounts even with kill -9 • still needs unprivileged user namespaces enabled; that is default on RHEL 8 4. singcvmfs on any system with singularity >= 3.4.0 • drop-in replacement for singularity; set environment variable with cvmfs repos to mount • requires container image to already be present (not read from cvmfs) • requires setuid-root singularity except when RHEL >= 7.8 and and singularity >= 3.6.0Consider also
- package building (at reconfig/upgreade)
- proxy search and setup (WPAD)