Can someone explain when this would be good solution? We currently store loads of files in S3 and directly ingest them on demand in our Java app API pods. Seems interesting if we could speed up retrievals for sure.

This looks super interesting for single-AZ systems (which are useful, and have their place).

But I can't find anything to support the use case for highly available (multi-AZ), scalable, production infrastructure. Specifically, a unified and consistent cache across geos (AZs in the AWS case, since this seems to be targeted at S3).

Without it, you're increasing costs somewhere in your organization - cross-AZ networking costs, increased cache sizes in each AZ to be available, increased compute and cache coherency costs across AZs to ensure the caches are always in sync, etc etc.

Any insight from the authors on how they handle these issue on their production systems at scale?