Peter Waller's https-redirect compiled against muslc, run with uid 99 (commonly "nobody") on port 3000.
That's it. Two files in a from-scratch image. No busybox or anything else.
Run it with:
docker run -d --name https-redirect -p 80:3000 dit4c/https-redirect
Don't trust my binary rootfs.tar.xz? Build your own with build_tarball.sh.