Comment by pmw

The most polished Glacier backup/restore mechanism I know -- because I helped build it -- is through rustic <https://rustic.cli.rs/docs/commands/init/cold_storage.html>. It has native support for backing up to Glacier (because writing to Glacier is identical to writing to regular S3), and it supports external "warmup" programs to support cold storage of your choice, with Glacier having an existing warmup program you can use.