HA was a thing long before "the internet" on mainframes, and still is. And apart from sharding, there were, and still are, load balancers for your service tier

HA was a thing long before "the internet" on mainframes, and still is. And apart from sharding, there were, and still are, load balancers for your service tier and HA (redundant, replicated) shared-disk DB clusters from Oracle and others around 1990 or earlier.