"Container" is simply a place where you can read the content today. That can be a HDD, it can be AWS, it can be a USB drive - doesn't matter as long as you have a system that can read it. Once that "container" starts to get near it's EOL you transfer it to a new "container".

I wouldn't trust a HDD for 20 years. Keep a backup mirror locally and a backup offsite (cloud or at a relative), what matter is that the transfer is automatically running in a periodic manner.