What is Redundancy?

Every system has parts that everything else depends on. One database. One load balancer. One machine running the service that authenticates users.

A part like that is called a single point of failure. When it stops, the whole system stops, no matter how healthy everything else is.

Redundancy is the fix. It means duplicating critical components or functions so that the system keeps working when one copy fails. That duplication buys three things at once: reliability, availability and fault tolerance.

The Simplest Version

Suppose your service runs as one instance in production