> Large HPC clusters are multi-tennant by nature, so running these containers needs to be rootless.
I can't see how any kind of sensible security evaluation process would reach that conclusion. If you trust your users you don't need rootless, if you don't trust your users rootless containers aren't good enough. I suspect people do rootless because it seems easy and catches a few accidental mistakes rather than it being a legitimate security measure.
Think R1 research university or government lab level HPC clusters…
These are almost always multi-tennant with differing levels of trust and experience between users. The data processed here can often have data access agreements or laws that limit who can see what data. You can’t have a poorly configured container exposing data, for example. So, the number of people who have root access is very limited. Normal users running workflows would all be required to run code rootless.
I can't see how any kind of sensible security evaluation process would reach that conclusion. If you trust your users you don't need rootless, if you don't trust your users rootless containers aren't good enough. I suspect people do rootless because it seems easy and catches a few accidental mistakes rather than it being a legitimate security measure.