I have Django code which creates a tar file on the fly from a list of requested files and works well. It doesn't use intermediate storage. The tar format can be pretty simple. I got most of the way into implementing a uncompressed zip version, but then I realised that tar was good enough for my site.

Mmm. If you had the right library, might be able to stream it as it’s being created which might help at least with perceived performance, but yeah, that’s a fun one.

I had to create streaming zips of files from S3 on the fly about 10 years ago, https://github.com/jonatron/django-s3-stream . I didn't find it fun.

Interesting, was there a business reason to not do that in the background somewhere?

Yeah, very non-technical users that won't check their email or click on a notification when the zip file is ready for them.

I can feel that deep in my bones.