What does 'eliminating single points of failure' mean in practice for a typical three-tier web application?

It means examining every layer for a component whose failure alone would cause an outage: multiple application replicas behind a load balancer (not one app instance), a load balancer that itself is redundant (most managed cloud load balancers already are, but self-hosted ones need an HA pair), a database with a replica and automated or fast manual failover (not a single unreplicated instance), and even DNS/networking paths and the deployment pipeline itself (a CI/CD system that's down shouldn't prevent emergency rollbacks). The exercise is recursive — fixing the obvious app-tier SPOF often rev