For large setups, the implementation is that you can have different fronted server (e.g. behind load balancing) and they access the same database and storage cluster. However, that is not just two servers.
Having a hot swap system ready, it’s a bit tricky if you want to have everything automatic. If you have just a second server in the background, that syncs data (e.g. like over rsync) and you sync the database as well, and if it is not critical to have the very latest data, then you can have a low tech solution. There are a few discussion on the forum to have to instances synced together: