Feature request: Singularity images for Dockerfile-based containers

[krokicki]

I recently added a couple of containers to BioContainers/containers: spark and stitching-spark. I used the Dockerfile route because I have no need to run Spark with Bioconda and because I'm not sure these would make sense to deploy into Bioconda.

My intention with these containers is to use them in Nextflow pipelines (e.g. lightsheetrecon) to create transient Spark clusters for large microscopy data processing.

The containers were successfully built and deployed to DockerHub:
https://hub.docker.com/r/biocontainers/stitching-spark
https://hub.docker.com/r/biocontainers/spark

However, they are not being converted to Singularity and made available on galaxyproject.org. My understanding based on the docs is this is intentional: it seems that BioConda images are pushed to quay.io and are then converted to Singularity, but Dockerfile-based images are pushed to DockerHub which is not scanned by this project.

I'm curious why this division exists and if it would it be possible to convert the Dockerfile-based images on DockerHub to Singularity as well?