Issue on E4S page: E4S Container Download

[maherou]

Please describe the problem with this page:

https://E4S-Project.github.io/container-download/

It seems to me that the E4S minimal images should really just contain Spack and nothing else. I don't see why we favor MPICH as something to pre-install. I think this is especially true for images that are more commonly used on laptops and may only want sequential execution or a single GPU execution. It would be very easy for the user to install MPICH just like anything else.

Perhaps we could provide a true minimal image with the 26.11 release that would contain only Spack.

[eugeneswalker]

It seems to me that the E4S minimal images should really just contain Spack and nothing else. I don't see why we favor MPICH as something to pre-install. I think this is especially true for images that are more commonly used on laptops and may only want sequential execution or a single GPU execution. It would be very easy for the user to install MPICH just like anything else.

This may have to be planned for after the 26.11 release. Our Spack build cache currently depends on MPICH coming from the system, as an external. This allows us to have a single MPICH for the entire, large E4S environment, where otherwise the environment would concretize to having multiple distinct MPICH specs. But, as a consequence, it's not so simple to just install MPICH on-demand for the subset of users who want to use it and MPI-dependent specs in the build cache. There are open issues relating to splicing and environment unification that have the potential to make it easier to have a single MPICH spec for the large environment while also allowing use of externals in target system install, and making it easy to use the build cache to do all of this.

[maherou]

Thanks for the update. I appreciate your constraints.

I don’t think this is a practical burden on users of the minimal image, just one that is conceptually confusing for users of E4S who don’t need MPI. As we go forward and expand the E4S user base to people who run on a single node or only use *CCL (NCCL, RCCL, OneCCL), including MPICH in the minimal container would strike them as strange, I think.

[eugeneswalker]

Yes, I understand. I agree-- it will be good to allow users to have a true minimal container image where they can quickly access only the packages they care about, from cache, including MPI if it is what they care about.