I am soon to lose my institutional HPC access, and want to port some of my projects to run on a commercial cloud. To avoid excessive costs, I only want to pay when I am using it, and not pay for any more resources than I need. Ideally, I would rent a high memory system for a short period of time in order to build genome indexes for STAR (which requires 64GB of memory, far more than any of my subsequent jobs should need). I also might need to provide other people with pre-built virtual machines that already have genome indexes built on them.
However, it seems that people recommend against using pre-built indexes. Or at least it was the overwhelming consensus in this thread: Pre made STAR Index?
So my question is: How I know when I need to build a new index? Every time I create a new installation? When I change versions of STAR? What kinds of problems can arise from pre-building a genome index?