Simplify variable symlink setup for users

[ocaisa]

We have an increasing number of variable symlinks which I suspect is going to get longer. It would be nice to have a helper script to set these up for people. I am thinking:

• Set up the basic variant symlink for host_injections
• Have the script create a default structure under /cvmfs/software.eessi.io/host_injections that covers
  • EESSI version-specific installations (/cvmfs/software.eessi.io/host_injections/2023.06, etc., for all EESSI versions under /cvmfs/software.eessi.io/versions)
  • GPU drivers under /cvmfs/software.eessi.io/host_injections/drivers
• Report back how variant symlinks should be set, and how to verify them
• Currently in our glibc we hard code some host paths, we should switch these to variant symlinks and do auto-discovery in the script
  • Current hard-coded paths can be replaced as default targets of the symlinks
  • Symlinks are only set if they are actually needed

[ocaisa]

You could take this a little further and suggest that people store all their CVMFS setup, including site customisation of CVMFS in the same folder:

# Choose the setup for the nodeset
subdir="default"
subdir_cvmfs_configurations="${subdir}"
installers="installer_group"
base_location="/path/to/shared_fs/cvmfs"
# Create your host_injections
mkdir -p ${base_location}/host_injections/${subdir}
# Change group ownership on the directory and make it persistent
chgrp ${installers} ${base_location}/host_injections/${subdir}
chmod g+ws ${base_location}/host_injections/${subdir}
# Add the variant symlinks
bash -c "echo 'EESSI_HOST_INJECTIONS=${base_location}/host_injections/${subdir}' > ${base_location}/domain.d/${subdir_cvmfs_configurations}/eessi.io.local"
sudo bash -c "echo 'EESSI_NVIDIA_OVERRIDE_DEFAULT=/cvmfs/software.eessi.io/host_injections/nvidia' >> ${base_location}/domain.d/${subdir_cvmfs_configurations}/eessi.io.local"

If you then have in your nodeset images

mkdir -p /etc/cvmfs/domain.d
ln -s /etc/cvmfs/domain.d/eessi.io.local ${base_location}/domain.d/${subdir_cvmfs_configurations}/eessi.io.local

then you don't need to touch node images to reconfigure CVMFS (but you would need to send them a sudo cvmfs_config reload software.eessi.io).

This would mean the admins retain control over CVMFS itself, but hand the keys of host_injections to another user/group (who don't need to worry about where /cvmfs/software.eessi.io/host_injections actually points). The use of /path/to/shared_fs/cvmfs/host_injections/${subdir} (or similar) also means you can have different setups for different node types.

[ocaisa]

@bedroge @casparvl I'm curious what you think about the above?