Software Reliability

A fault is defined as a component of a system deviating from its spec. A failure is when the system as a whole stops providing the required service to the user. Systems that can anticipate faults and cope with them are fault-tolerant or resilient. Obviously, we can't anticipate every type of fault so it only makes sense to talk about certain types.

Hardware

• Hard disks have a mean time to failure (MTTF) of about 10 to 50 years
• Redundancy and dual power supplies help
• So does moving away from single-server systems

Software

• Software bugs
• Runaway processes
• Third-Party API failures

Carefully thinking about assumption and interactions made in the software can help

Humans

• Understand that all humans are unreliable
• Design systems that minimizes opportunity for error.
• Decouple the places where people make the most mistakes from the places that cause system failures
• Test thoroughly at all levels
• Set up monitoring/logs

Some tools exist to try and trigger faults as a way to see where the weak points in the application are.

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This post was based on the book Designing Data-Intensive Applications by Martin Kleppmann.