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Reliable, Scalable and Maintainable Applications

A roundup

An application meets multiple requirements to be useful. There are functional requirements (what it should do). And there are non functional requirements (general properties like security,  reliability, scalability, maintainability)

Reliability means making systems work correctly, even when faults occur. Faults can be in hardware , software, humans

Scalability

This means keeping performance good even when load increases.  In scalable system you can add processing capacity in order to remain reliable under high load

Maintainability

It is about making life better for engineering and ops team who work on the system. Good abstractions reduce complexity. Good operability means having good visibility to system health..