Failover. Surviving a failure

Single points of failure: a second load balancer, a read replica that takes over the database, health checks, failover, and availability versus durability.

Diagram of failover: a load balancer and a database have failed, and traffic flows on through their standby pair, leaving no single point of failure.

System Design — Load balancers, caches, queues and regions: build a system that holds the load