What is Availability and Downtime? How to design for high availability? Design for HA

Availability is to make your products, services, and tools available to your customers and employees at any time from anywhere using any device with an internet connection.
And
Downtime is the time during which a computer or IT system is unavailable, offline or not operational.

Usually, we design a system for high availability. For example, when we say the design target is 4-9’s, it means the services should be up 99.99% of the time. This also means the services can only be down for 52.5 minutes per year.

Even with 90% availability on the cloud we can try to achieve 99% availability with this double node architecture.